I know some eye tubes are sort of scarce, but I would expect you'd be able to find replacements. If nothing else, I would expect Cary would sell you a tube. I'll bet the guys at VTV would too, and now that I think about it, there are probably plenty of other sources.

Have you seen Eric Barbour's article on eye tubes? If you haven't already seen it, check it out - It's interesting and has some great information.