The Free On-line Dictionary of Computing (30 December 2018):

TLAs

    As of 2014-08-14, this dictionary included 1285
   three-letter acronyms, which is 7% of the 26^3 = 17576 possible.

   Here's a grep command to find them:

   	egrep '^[A-Z][A-Z][A-Z]$' Dictionary

   or a GNU Emacs command:

   	(occur "^[A-Z][A-Z][A-Z]$")

   Here they are:

   AAC, AAL, AAP, ABC, ABI, ABM, ABP, ABR, ACA,
   ACE, ACF, ACK, ACL, ACM, ACP, ACT, ADC, ADL,
   ADM, ADO, ADR, ADS, ADT, AED, AEP, AES, AFJ,
   AFK, AFP, AFS, AGL, AGP, AIA, AID, AIR, AIT,
   AIX, AKC, AKL, ALC, ALF, ALM, ALP, ALU, AMD,
   AMI, AML, AMO, AMP, AMS, AND, ANI, ANL, ANR,
   ANS, ANU, AOL, AOP, AOS, APA, APC, APE, API,
   APL, APM, APT, AQL, ARC, ARL, ARM, ARP, ARQ,
   ART, ASA, ASE, ASF, ASK, ASL, ASM, ASN, ASP,
   ASR, AST, ATA, ATK, ATM, ATS, ATX, AUI, AUP,
   AVC, AVI, AVS, AWE, AWG, AWT, AYT, BAD, BAL,
   BAP, BBC, BBL, BBS, BCC, BCD, BCL, BCS, BDC,
   BDL, BEA, BEG, BEL, BER, BFI, BGA, BGP, BIP,
   BLT, BMF, BMP, BNC, BNF, BOA, BOF, BOS, BPI,
   BPR, BPS, BQS, BRB, BRH, BRI, BRS, BSA, BSD,
   BSI, BSL, BSS, BST, BTB, BTS, BTW, BWQ, CAD,
   CAE, CAF, CAI, CAL, CAM, CAN, CAP, CAR, CAS,
   CAT, CAV, CBD, CBN, CBR, CBT, CBV, CCD, CCL,
   CCP, CCR, CCS, CDA, CDC, CDE, CDF, CDL, CDM,
   CDR, CDS, CDW, CEN, CER, CFD, CFP, CGA, CGI,
   CGM, CHI, CID, CIF, CIL, CIM, CIO, CIR, CIS,
   CIX, CJK, CLI, CLM, CLP, CLR, CLU, CLV, CLX,
   CMA, CMC, CML, CMM, CMP, CMS, CMU, CMZ, CNC,
   CNI, CNN, CNR, COM, COS, CPE, CPI, CPL, CPM,
   CPS, CPU, CRC, CRL, CRM, CRT, CSG, CSL, CSM,
   CSO, CSP, CSR, CSS, CSU, CSV, CTC, CTI, CTL,
   CTS, CTY, CUA, CUL, CUT, CVS, CWI, DAA, DAC,
   DAG, DAS, DAT, DAU, DBA, DBC, DBH, DCA, DCC,
   DCE, DCG, DCI, DCL, DCP, DCS, DCT, DDB, DDE,
   DDL, DDM, DDN, DDO, DDP, DDR, DDS, DDT, DDW,
   DEA, DEC, DED, DEK, DER, DES, DEX, DFA, DFC,
   DFD, DFS, DFT, DGL, DIB, DID, DIL, DIM, DIN,
   DIP, DLC, DLE, DLG, DLL, DLM, DLP, DLT, DMA,
   DME, DMI, DML, DMM, DMS, DMU, DMZ, DNF, DNS,
   DOA, DOE, DOF, DOL, DOM, DOS, DPA, DPB, DPL,
   DPN, DPP, DPS, DRM, DSA, DSE, DSI, DSL, DSM,
   DSN, DSO, DSP, DSR, DSS, DST, DSU, DSW, DTD,
   DTE, DTP, DTR, DTS, DUA, DVD, DVI, DXF, EAF,
   EAG, EAI, EAX, ECC, ECL, ECM, ECP, EDA, EDF,
   EDI, EDL, EDM, EDP, EDS, EER, EFF, EFI, EFL,
   EFT, EGA, EGP, EIA, EJB, ELF, ELI, ELP, EMA,
   EMC, EMI, EML, EMM, EMS, EMX, ENQ, ENS, EOF,
   EOL, EOR, EOT, EOU, EPL, EPP, EPS, ERA, ERC,
   ERD, ERM, ERP, ESA, ESC, ESD, ESF, ESI, ESL,
   ESP, ESR, ETB, ETC, ETL, ETM, ETX, EVE, EXE,
   FAC, FAD, FAP, FAQ, FAT, FCB, FCP, FCS, FDC,
   FDD, FDT, FEA, FEC, FED, FEL, FFP, FFT, FGL,
   FHS, FIR, FIX, FLI, FMQ, FMS, FMV, FNC, FOD,
   FPA, FPM, FPU, FQL, FRA, FRL, FSB, FSF, FSK,
   FSL, FSM, FSP, FTP, FTW, FTX, FUD, FXO, FXS,
   FYA, FYI, GAL, GAN, GAP, GAT, GCC, GCL, GCR,
   GCT, GDA, GDB, GDI, GEA, GEI, GEM, GFR, GFS,
   GHC, GIF, GIN, GIP, GIS, GKS, GLB, GLS, GLU,
   GMD, GMT, GNN, GNU, GOL, GOM, GPF, GPL, GPM,
   GPS, GPV, GPX, GRE, GRG, GSI, GSL, GSM, GSS,
   GTL, GUI, GVL, GWM, HAL, HCF, HCI, HCS, HDA,
   HDC, HDD, HDF, HDL, HDM, HEP, HFC, HID, HLL,
   HMA, HMP, HNC, HOL, HPF, HPL, HPR, HSB, HSC,
   HSM, HSV, HTH, HVD, IAB, IAD, IAL, IAM, IAP,
   IAR, IAS, IAW, IBM, ICA, ICE, ICI, ICL, ICQ,
   ICT, ICW, IDD, IDE, IDL, IEC, IEF, IEN, IFC,
   IFF, IFP, IFS, IFX, IGC, IGL, IGP, IGS, IGU,
   IHS, IHV, IIL, IIR, IIS, IIT, ILF, IMD, IML,
   IMO, IMP, IMR, IMS, IOI, IOS, IOW, IPA, IPC,
   IPE, IPL, IPS, IPT, IPX, IQL, IRC, IRL, IRM,
   IRQ, ISA, ISE, ISF, ISL, ISO, ISP, IST, ISV,
   ITP, ITS, ITU, IVR, IVY, IXC, IXO, JAD, JAZ,
   JCL, JCP, JDK, JES, JIT, JMS, JNI, JPL, JRE,
   JRL, JRN, JSA, JSF, JSP, JTB, JTC, JTS, JVM,
   KAP, KBS, KCL, KEE, KFX, KIS, KLB, KMS, KNI,
   KRC, KRL, KRS, KSL, KSR, KTH, KVM, LAN, LAP,
   LAT, LAU, LAX, LBA, LBE, LBL, LBX, LCC, LCD,
   LCF, LCL, LCP, LCS, LDB, LDL, LDP, LDT, LEC,
   LED, LEO, LER, LGN, LIF, LIS, LKA, LLC, LLP,
   LML, LNF, LOC, LOL, LOM, LOP, LPC, LPF, LPG,
   LPI, LPL, LPS, LPT, LRC, LRU, LSA, LSB, LSE,
   LSL, LSP, LSR, LTL, LTR, LUG, LUN, LVD, LWP,
   MAC, MAD, MAL, MAN, MAO, MAP, MAS, MAU, MBS,
   MCA, MCC, MCI, MCL, MCP, MCS, MDA, MDF, MDI,
   MDL, MFC, MFE, MFM, MHS, MIB, MIF, MIG, MII,
   MIS, MIT, MIX, MJS, MLL, MMI, MML, MMO, MMS,
   MMU, MMX, MNP, MOO, MOS, MPC, MPG, MPI, MPL,
   MPP, MPV, MPX, MQG, MRI, MRP, MRS, MSB, MSM,
   MSN, MSS, MSX, MTA, MTS, MTU, MUA, MUD, MUP,
   MVC, MVS, MXI, NAG, NAK, NAS, NAT, NAU, NBS,
   NBT, NCD, NCP, NCS, NDL, NDS, NEC, NFA, NFS,
   NFT, NGL, NIC, NIH, NII, NIL, NIS, NLM, NLP,
   NLS, NLX, NMI, NMU, NNI, NOC, NOL, NOR, NOS,
   NOT, NPC, NPL, NQS, NRZ, NSE, NSF, NSI, NSS,
   NTP, NTU, NVL, NVS, OAP, OBE, OBJ, OCL, OCP,
   OCR, OCS, OCX, ODA, ODC, ODI, ODP, ODS, ODT,
   OEM, OFA, OIC, OID, OIL, OLC, OLE, OMA, OMF,
   OMG, OMR, OMS, OMT, ONC, OOA, OOD, OOF, OOP,
   OPC, OPF, OPS, ORB, ORM, OSA, OSD, OSE, OSF,
   OSI, OSP, OTI, OTP, OTT, OWL, PAD, PAL, PAM,
   PAP, PAT, PAW, PBD, PBM, PBX, PCA, PCB, PCF,
   PCI, PCL, PCM, PCN, PCS, PCU, PDA, PDC, PDF,
   PDH, PDL, PDM, PDP, PDS, PDU, PEM, PEP, PER,
   PEX, PFE, PFL, PFP, PGA, PGP, PHP, PIC, PID,
   PIE, PIL, PIM, PIN, PIP, PIT, PKE, PKI, PLC,
   PLD, PLL, PMC, PML, PMP, PNG, PNP, POA, POC,
   POE, POM, POP, POR, POS, PPC, PPD, PPL, PPM,
   PPN, PPP, PQS, PRA, PRI, PRL, PSA, PSD, PSF,
   PSI, PSK, PSL, PSN, PSO, PSU, PTF, PTI, PTN,
   PTT, PUB, PVC, PVM, PWM, QAM, QBE, QCA, QIC,
   QMW, QNX, QPE, RAD, RAL, RAM, RAS, RCC, RCL,
   RCS, RDF, RDI, RDL, RDP, RDS, REC, REM, REP,
   REX, RFC, RFE, RFI, RFP, RFT, RGB, RIP, RJE,
   RKM, RLE, RLF, RLL, RMI, RMS, RNF, ROM, RPC,
   RPG, RPI, RPL, RPM, RPN, RPT, RRL, RRS, RSA,
   RSI, RSL, RSN, RSS, RTF, RTI, RTL, RTM, RTP,
   RTS, RTT, RWP, SAA, SAC, SAD, SAL, SAM, SAN,
   SAP, SAR, SAS, SBD, SBE, SBM, SBR, SCA, SCC,
   SCI, SCL, SCM, SCO, SDE, SDF, SDH, SDI, SDK,
   SDL, SDM, SDP, SDS, SEA, SEC, SED, SEE, SEI,
   SEL, SEM, SEP, SET, SEX, SFA, SFL, SGI, SHA,
   SIA, SIG, SIL, SIM, SIP, SIR, SKU, SMB, SMG,
   SMI, SML, SMM, SMP, SMS, SMT, SNA, SNI, SNR,
   SOA, SOE, SOH, SOJ, SOL, SOM, SOS, SPC, SPD,
   SPE, SPG, SPI, SPL, SPM, SPS, SPX, SQE, SQL,
   SQR, SRI, SRL, SRP, SSA, SSD, SSE, SSI, SSL,
   SSO, SSR, STB, STD, STP, STX, SUB, SVC, SVG,
   SVS, SWL, SWT, SYN, TAA, TAB, TAC, TAL, TAO,
   TAP, TBF, TBK, TCB, TCM, TCO, TCP, TDD, TDF,
   TDI, TDM, TDR, TEI, TET, TFT, TGA, TIA, TIP,
   TLA, TLB, TLD, TLI, TLS, TMG, TNC, TNX, TOK,
   TOP, TOS, TPA, TPF, TPL, TPO, TPS, TPU, TPX,
   TRO, TRS, TSO, TSP, TSR, TSV, TTD, TTL, TTS,
   TUB, TUI, TXL, UAN, UAT, UAW, UBD, UCB, UCP,
   UCS, UCX, UDF, UDP, UFO, UIL, UIS, UKC, ULP,
   UMB, UML, UNC, UNI, UPS, URC, URI, URL, URN,
   USB, USE, USL, USP, USR, UTC, UTF, UTP, VAL,
   VAN, VAR, VAX, VBA, VCD, VCL, VCR, VDL, VDM,
   VDT, VDU, VEE, VEL, VGA, VGX, VHE, VHS, VIF,
   VIM, VLB, VLM, VME, VML, VMS, VOS, VPL, VPN,
   VQF, VRC, VSE, VSF, VSP, VSX, VTC, VTS, VTW,
   VUE, VUP, VXI, WAM, WAN, WAP, WBS, WCL, WDM,
   WEB, WEP, WFL, WFW, WGL, WIC, WLL, WMA, WMI,
   WML, WMV, WOM, WPA, WPG, WPI, WRT, WSL, WTF,
   WTH, WWW, XDL, XDR, XFS, XGA, XIE, XML, XMM,
   XMS, XNF, XNS, XON, XPC, XPG, XPL, XRN, XSB,
   XSD, XSI, XSL, XTI, XTP, XUI, XUL, XVT, XXX,
   YSM, ZAP, ZFC, ZIF, ZIL, ZOG, ZUG

   (2014-08-14)