WordNet (r) 3.0 (2006):

fall upon
    v 1: find unexpectedly; "the archeologists chanced upon an old
         tomb"; "she struck a goldmine"; "The hikers finally struck
         the main path to the lake" [syn: fall upon, strike,
         come upon, light upon, chance upon, come across,
         chance on, happen upon, attain, discover]

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "fall upon":
   alight upon, ambush, appear unexpectedly, arrive at, arrive upon,
   assail, assault, attack, be unexpected, blitz, bob up, bump into,
   bushwhack, come across, come among, come at, come down on,
   come unawares, come up against, come upon, confront, crack down on,
   creep up on, descend on, descend upon, drop on, encounter,
   fall across, fall among, fall foul of, fall on, flash upon one,
   gang up on, get at, go at, go for, harry, have at, hit,
   hit like lightning, hit upon, jump, land on, lay at, lay hands on,
   lay into, light into, light upon, meet, meet head-on, meet up with,
   meet with, mug, pitch into, pitch upon, pop up, pounce upon, pound,
   reach, run across, run into, run smack into, run up against,
   run upon, sail into, set on, set upon, settle on, strike,
   strike upon, stumble on, stumble upon, surprise, swoop down on,
   take the offensive, turn up, wade into