I just got a nice set of Continental 27" tires for my Velo Cheap project.
All the LBSs in my part of town stock 27" x 1/14. The harder sizes to find are 27" x 1/8" and 27" x 1" but those are around too. One of them is the same size as a 700c- I think its the 1" width like I use on my Schwinn Sports Tourer.