Take it to a vet. The vet will know what's going on, and no respectable vet would just toss it. If you tell the vet you'd like to bury your kitty, they'll put it down, and give it back to you. That said, all the cats I've ever had just ran away and died, so I've never taken one to a vet to get put down, so I'm just guessing. I hope your kitty is all right.
