I am also looking for a replacement. My display failed a few weeks after the warranty expired and I would like to fix it myself IF I could find/buy a replacement. Any pointers would be appreciated.
After much digging around I found the part on eBay "661-6048, 661-5543 Power Supply 250W Apple A1407 Thunderbolt Display (27-inch)".
I had no idea whether it would work or not but decided to give it a go and it worked.
The board itself was visibly different to the board that it was replacing (some of the components were different, capacitors etc.) which worried me but it definitely worked.
DM me if you want the link on eBay.