FHA really isn't credit score driven, it's the Banks and Lenders that set those score requirements. There are a few lenders that go down to 580 with FHA, I personally have closed on several homes with clients around and under 600. I recommend all my clients that have credit issues to check with The Lenders Network, check them out. If anyone can get you approved they can!
You are pretty close to getting a rural housing loan which is 620. Have you had a lender look at it and see if there is something that you could do to get it up some? There actually is a lender here in Jackson that does lending as low as 580 if you fit their criteria. Shoot me an email. email@example.com
I'll help you figure out what lender to try.