Go to http://www.speakerhold.com they have a x audio sub actully two one resebles a Kicker L7 the only copy there is of the L7 and a 15 inch sub both look decent never heard the though.
I am actually looking for the brand x audio....and they do make subs, they don't have too many in their line, but there are a few. If you want to look at them at all, go to speakerhole.com I was just looking for another site that has them or reviews on the subs. Thanks though