My experience with cat rescues is very poor. My only advice is to try a PetSmart store with an adoption section and try finding a Veterinarian that places kitties.
Yes, many vet’s offices have notice boards where you can post lost/found pets and pets in need of a home. Very good suggestion.
Brother’s vet put kittens for sale but the payment goes for first yr of services.
Cat rescues work best when kittens or a bit older, but that old is far more difficult. Unfortunately. If the cats still have claws, you might try a farm place where the farmer will take the cats and they can fend for themselves, rather than being killed. We have cats all the time, love em and spoil them, and I pray for a good solution for you.
Our last four cats have come from a Petsmart program - a local volunteer rescue organization works with them.
Previous to that, I found a wonderful cat by looking in the want-ads. This was before the Internet, so I don’t know how individuals with a litter of kittens advertise them now; but in those days, people would advertise kittens and give them away for free.
Bulletin boards in vet offices are another good idea - lots of people who have had to euthanize their cats will be looking for another one.