I'm so sorry to hear of your loss. But 18 years is a wonderful life! My childhood cat, Tigger, lived to be 18. He died in his sleep.
I know if you look in the classified ads of your local paper, you should find hundreds of free kittens. It's a shame, but they will be there. Good luck and share your story with us when you find the right one. Hope you'll find one at a shelter or from a good home. Can't wait to hear about it.