If you need 27" wheels, Weinmann sells some, also Sun. Velocity has some 27" rims but they aren't cheap. Rivbike.com and Velo-orange.com sell brakes that will fit 27" wheel frames. Rivendell's version of the long reach Tektros is called "Silver" and looks very nice plus has very good Kool-stop brake pads. Dia-Compe makes a centerpull brake that has a long reach, too. I've used both of these brakes on bikes and they work well.

On my Raleigh Sprite, I had to use the long reach brakes even though I put 27" wheels back on it.

Depending on how old the bike is, you may just need 700c. Might want to ask your LBS if you can't tell.