you might want to contact the local shelters to see if there are any spay/neuter programs for feral cats? We have the staff of spca volunteering one day a year to spay and neuter trapped feral cats. Last year it was canceled due to low number of cats (though I don't quite believe that).

I would try what others suggested, in trapping and getting them fixed yourself. You can always borrow traps from veterinarians or shelters.

In Japan, hardly anyone ever spays/neuters their cats, so they are totally overrun with cats. My mother's trapped a lot of the cats in her neighbourhood and had them fixed and then released again (all out of her own pocket).