I like Helboys sleeve:
Not really MMA....but I relate it to being MMA because I know who he is.
Check out all of Gilbert Yvel's and Aleks Emelianenko's tats if you haven't.
I think Aleks got some coverups though:
I thought I remember him having some cool tats on his arms. Back tat is crazy....but probably not your cup of tee.
Tons of pics on Yvel, just not many closeups. I only searched for 2 minutes....so you might have better luck.