You mean the frame transistors, right? I just installed some of these in one of my 6100's:
http://www.digikey.com/product-search/en?keywords=36-4606-ND
I wanted these ones because they have the holes that allow you to bolt them to the frame (which the holes are already there for, but were never used). These are much nicer for replacing bad transistors in the future, as the socket stays attached to the frame, and you don't have to fumble with it. I also use the silicone thermal pads, and you can replace a transistor in about a minute, without having to mess with thermal grease, mica, and all of that. Here are the pads:
http://www.digikey.com/product-detail/en/bergquist/SP400-0.007-00-05/BER203-ND/529920
The only issue I had with the sockets above is that they rely on the mounting holes (which keep them bolted to the frame) to do the aligning, whereas the original sockets have raised bits of plastic around the transistor pins, which align the socket with the holes. You need to make sure the small screws you use to bolt the socket to the frame are pretty much the exact hole size, otherwise the socket can slop around, and you have to align them manually, as there is some play.
I just used some screws I had on hand, but they were a little too small, so there is some play, but I just visually got them aligned, then tightened them down (and I test for case shorts after I replace a transistor anyway, before applying power). But if you got the right screws (sorry I don't have a link), or used rivets like they did on the b/w vector monitors, they would align better, with no slop.