Tom, I just read your introduction post, and what a wonderful story!
Cats are so smart, and they definitely choose their humans.
I'm so sorry your kitty is sick. Sending loads of healing vibes Hey's way.
As to a vet, there are a number of things you can do.
As Sharky suggested, you can call around to local shelters and explain the situation.
You can also call local vets to talk about pricing, special pricing for those with fixed incomes, or potentially a payment plan.
Our vet was aware of local funding for people with limited resources, and we were there with our kitties one day when they helped a woman get funding for her kitty to be catheterized because her male kitty's urethra was blocked - there may be other vets out there that know where to turn for help in situations like this.
Apart from the yellow pages, a GREAT place to help you look is this site:http://www.pets911.com/services/veterinarians/index.php
I looked up a zipcode for Oklahoma City and plugged it in - if your zip isn't 73104, you can plug in the correct zip code and then click any of the buttons on the left - for a list of veterinarians, for a list of shelters/rescue organizations - and then let your fingers do the walking.
It may take a little work on your part, but don't give up. Vets are businesses, and shelters are in a way as well - but there are people out there that want to help when and if they can, it's just a matter of finding the right place.
Just remember - pets911 provides information for people with many types of animals, so just ignore the equine docs or the ferret rescues.
Hope this helps,