I am building a commuter--kind of like the European ones from the '40s and '50s. I have Nitto promenade bars which are 25.4mm, and I don't really know where to start looking for brake levers. Is 25.4mm a standard size for a particular type of lever (MTB, BMX...), do some levers have adjustable clamps? What should I be looking for?
Most brake levers come with rubber or metal shims, so don't worry too much about the diameter. As for a decent set of levers, you might try NYC bikes. I don't know if it's what you're looking for, but I just saw an extremely cheap set there. 2 Tektro levers for 2 dollars.