Aimee,
I know how you feel - we had a cat out in our neighborhood for several
years who kept having kittens. We finally trapped her last summer :-) I
persuaded her caretaker to feed her in the open trap for several weeks,
but whenever he set the trap she somehow knew and didn't go inside. Of
course her caretaker felt sorry and never let her go hungry for more
than 36 hours, so there really was no need ;-) Finally I threatened not
to help him any more at all, so we fed the rest of the colony every day
and shoed her away (she is by far the most fearful of the crowd). On
the third evening, we fed everyone canned food till they wanted no more
(so they wouldn't be tempted by the trap) and laid a trail of small
pieces of honey baked ham into the trap. 10 minutes later we had her
and she went directly to the vet for her spay.
Good luck!