Bicycle Mechanics - Front Derailleur clamp size question

My current road bike has a 1-3/8" / 34.99 mm tube and I'm having trouble finding the right sized clamp on a FD to fit it when I upgrade. Can I just buy the derailleur that I want and just reuse the current clamp that I have that fits?

That is a fairly common size, you should be able to find it at most LBS.. I know that is what one of my bikes takes I had no problem finding one. I really doubt you could re-use the old clamp.

If you have a braze on style der. where the der bolts to a clamp that fits the frame, then yes you can just buy a braze on der. and put it on your existing clamp.
i just checked the catalog, QBP, and there arn't any 1 3/8 road der.(For shimano, campy does offer them) so you must have the braze on style.

http://www.performancebike.com/shop/Profile.cfm?SKU=150 Performance Bike sells a clamp that big (1-3/8"), I just figured that all of the Shimano FDs all used the same clamp in varying sizes.

Right, you get a clamp and a braze on der. If you had a smaller frame you could get a der. that has a clamp that is part of the der. they only go up to 31.8

Nashbar has this :: http://www.nashbar.com/profile.cfm?category=83&subcategory=1038&brand=&sku=2189&storetype=&estoreid=

They look like different products to me.

The Performance clamp looks like a replacement clamp for a broken one (Maybe) or a replacement one for situations such as mine.

The Nashbar clamp looks like what you're describing.

The Shimano one is the one for you but if you allready have a der on your bike then you have the clamp. You just need to get a Shimano braze on der.
Some bikes esp. older steel bikes have a tab called a braze on (other things are called that as well) that the der bolts to rather than using a band clamp. The nashbar part is for when that breaks, altho I would just braze a new one on (which is why all the little bits tacked on to a frame are called braze on even tho now adays most parts are welded, bonded, or bolted on.)