Lookin for Clam suggestions...

[revgeoff]

Ok, now that I am pouring every spare cent into converting my 120 gal into a reef (I hope my son doesn't want to go to university) I have decided that I would like a clam as well...
I have the 24" deep 120gal and 2x175w MH lights. Can anyone tell me what clams I can keep and where I can pick them up. All I have seen over the last couple of months are Maximas and I think I would need 250s for those.
As all I have picked up are frags, I have a lot of space either on the sandbed or high up in the rock.
Thanks in advance for any help!