First I commend you for wanting to do this. And yes call around the shelters and rescues to find out who they use. In GA there were a couple of mobile units. I used CatSnip.. Drop them off early in the morning and pick them up later that afternoon. And ferals I think they did for free. Too bad not all places have things like this. It would make for many more animals getting fixed. My other pet peeve is the vet charging $50 for microchipping. It can be done WAY cheaper than that.