If you're looking for jamma-only, there's a Jamma loom on ebay right now. If you're after the -001 jvs/jamma loom like I am, they seem to be relatively difficult to find. At least for a < 150 price.
I have had bad experience with him ... what you see is not always what you get ... so I prefer other options.
if you look at
http://wiki.arcadeotaku.com/w/Sega_Blast_City_Wiring_Guide, you'll see that the #600-6738-21 he is advertising does NOT have the RCA plugs ... cause it's actually the jamma/jvs #600-7143-001 ... or the "jamma lindberg" as he calls it.
either way, he's not getting my money !
oh .. and he says he's from ontario Canada but stuff comes from China ... so another notch on the bed post.