Your best bet is to cannibalize a FAT PS3. You can find broken ones locally or on the net for very cheap. I haven't heard of third party PS3 internal cable suppliers. But some of the fan/other cables look almost identical to the ones that plug into motherboards aside from the cable colors. But for the price you can buy a bunch of 2 and 3 pin fans for PCs you can get a dead PS3. The other route you can go is soldering the connections, doesn't really matter the connection type then right ?
Hope this helps a little.
CECH2501A-750GB Rebug 4.46.1 / CECHG01-250GB Kmeaw 3.55 / 2TB External / PSPGO 6.60 PRO-B10 / PS2 v2