The one and only 64 FX chip I know of that was still available is now in the hands of another forum's user that me and
@Robert B frequent. I know this as the mainboard he managed to install it into came from me - it's a nForce 3 250 based Gigabyte GA-K8NSC-939. I had two of them and sent them both to him, mostly because I'm not very invested in AGP stuff as he is - I can easily say this as AGP cards are a whole 'nother level of can of worms to open. He is also the one who helped me find the x2 4600+ I'm currently running by the way, although the 939 x2 3800+ was a suggestion on the classified site he found the 4600 on. Didn't buy the 3800+ as the seller had a "minimum price to ship" policy and I wasn't going to get a 4th AM2 chip just for that. (and he wasn't sure if he still had the 939 chip either)
As for 64 x2 chips - the only ones that are widely available here are Brisbanes for the most part, though I'm not fully certain if I do have a Windsor - I have a 3800+, a 4200+ and a 5200+ for AM2 - I can surely tell the 5200 is a Brisbane. The ones I'm not fully certain of are the 3800+ and 4200+.
939 dual cores are short of extinct unless you have as close relations with people around flea markets and recycling centers as
@Robert B has, here in Romania. AM2s are slowly going the same way too - the most AMD dual cores I'm seeing nowadays are AM3 stuff at best - Athlon IIs, Phenom IIs, you name it.
Oh, and FX (Bulldozer/Piledriver) chips - the only ones that don't really seem to be selling that well are the Zambezi chips - no wonder, the 4100 I have was so bad that even a i3 540 stomped it. Yes, even a i3 540 managed to outperform that 4100. It killed itself for whatever reason when I tried to run it on a ASRock mainboard that originally had a 8300 - the mobo still works, it still accepts other FX chips - it's just the 4100 that quietly died - not that I'm sorry for that chip's death - I have a 4300 and a 8300 that better than it (at least the 4300 does - no idea why the 8300 has so bad performance in as little as NFS Hot Pursuit 2010.)
As for the PSU - I'm already on the hunt for a 3rd unit that would sport 2x 6+2 PCI-E cables - I figured I should do this as the 8800GTX might be my only choice if I can't get sound working by any means through the 8600GT. For the time being though, I'll be running the chip on one of the Spire Jewel SP-ATX-420WTN-PFC units I have. The newer one I have (~2010 datecode) was properly serivced by me (someone tried to replace the secondary caps but gave up, and the fan was seized on top of that) and I can trust it to power as much as a Quadro FX3700 at best - it powered a HD4850 + Q6600 without much hassle and was barely warm during the whole time it was on.