Where can I get the right replacement cats?

OK so I have a BBK h-pipe with Cats that I bought used and now one of the cats is rattling and needs to be replaced. I was wondering if anyone knows where to get some that will swap right in. I looked in summit and the ones I could find were like 16 inches long and the ones on their now are only 10 inches long. ANy ideas? Thanks,

I never thought anyone would respond to this LOL. But I actually already bought a new magnaflow one off Jegs last wk. Havent installed it yet cause it just showed up sat but looks pretty nice. Let me see if I can find the one I bought.

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=84491&prmenbr=361

it's the 2.5 inch one with the air tube. Only thing is the air tube turns where ours come straight out so I dont know how they'll handle that just yet. But I figure they can just cut it and put a new one on.