Someone correct me if this is bad advice, but I would think that any 27" or 700 tube would work, provided the stem (presta, schraeder, ...) matched the drilling in the rim. However, you'll want tubes for the wider dimensions (e.g. 35, as lostarchitect suggested, is a wider tube/tire), as there are narrower ones for racing tires.

The diameter of a "700c" -- 622 -- and '27"' -- 630 are so close (8mm) that they are effectively interchangeable. This is rubber we're talking about after all.