Bought car, now no title

What can you do about a guy who sells you a car and tells you he has the title, but after you take delivery of the car he says he can't find the title ? When I paid for the car he said he would get the title notorized and give it to me in a couple of days. It's now been 2 months and he says he can't find the title and is no hurry to do anything about it. I live in Oklahoma, so does he. It seems like this should be illegal in some way. I trusted this guy, and have already done extensive work to the car, so I don't want to give it back. Any ideas about what I can do about this ???