I was thinking about building a bike from the ground up and was wondering where I could get a tube set.
http://www.framebuilding.com/ http://www.cycle-frames.com/bicycle-frame-tubing/
You might like the Framebuilders group https://groups.google.com/group/framebuilders/about
It just moved to Google groups a month ago You can search many years of postings at the old location http://www.phred.org/pipermail/framebuilders/
Also I posted a boatload of framebuilding links in this old thread http://www.fluther.com/89336/i-want-to-make-bicycles-am-i-crazy/
Good luck! That is a great endeavor!
You can get them at any bicyclle shop and I have aso seen them at Walmart.
@kitkat25 , I think the OP is asking about the tubes used in frame construction, not inner tubes. Although I haven’t been to Walmart recently, so I don’t know what they’re carrying.