I know that there are supposedly non-bike specific(read:less expensive) tools available to ream out a seat tube to 27.2, but I haven't had any luck locating where to purchase one. Anyone got a good link?
Remember, seat tube reamers are designed to remove a distortion in the tube, not adjust tube diameter. To get a 27.2 tube, you need three things: A 27.2 tube to start with; B a reamer to remove internal distortions, and good technique with the torch to start with; C or sleeve the area so that heat distortion does not affect the tube in the first place.
I once built a frame using a True Temper double butted seat tube. The tube was .8 mm thick at the top so I took my reamer after the frame was built and took it down to .65 or so until a 27.2 mm seat post fit. No biggie, even reaming a heat treated tube.
Becareful buying/selling bike parts on-line. I learned the hard way. :(
Sure the expanding reamers cover a range, but it isn't ideal. If the tube is straight and correct diameter but has a couple of bumps in it, or a slight bend at the top, it is one thing to get that out. It is another to use a latheral curring reamer that may be shorter than the section one wants true to link sections together that are greater than it's length. For me when I use standard size tubes I use the 26.8 seat post rather than try to ream out the tube.