I'm right there with you -- four of my five cats are rescues.
You might want to contact this organization:
Alley Cat Allies
Alley Cat Allies - Contact Us
They have a huge campaign to get feral and stray cats neutered and then returned to where they were found with neighbors feeding them. Once the cats are neutered, no more kittens. Yay! This system works 100 times better than getting them into a shelter and then killing them.
You don't need money to help. They need people to write letters and emails to mayors and other village people all over the US to let them know about this program -- Trap-Neuter-Return (TNR). Contact them to find out how to help.