You can try WWW.frys.com (sorry for no hyperlink but I'm typing this on my cell phone) they should have everything that you will need and miyht even sell by the hundred foot spoils if you really want . Hope this helps but If not let me know qnd I will find the site on my computer that I used to buy my stuff back when I was In school for computer and electronic engineering.
I have found the following web sites that outline the power connectors.
ATX 24 pin pin out
Wire gauge diagram of 20 pin ATX power (which is just a 24 pin minus 1x 3.3v, 5v, 12v, and ground)
All in all, it seems that 18ga wire is more than enough to do anything that is in a computer, I think just like the old speaker boxes of the past, "the bigger the better" is in effect when it comes to Ultra's X4 cabling.
I have all the cables done up and sleeved, if they don't work, I will just make them into SATA, Molex, PCIe, etc. and use the stock 24 pin until I can do something right.
One question on the pins I have, they are perfect for a 18ga wire, are there ATX pins that are made for 16ga wire instead?
Edited by Covertop - 8/13/10 at 11:37am