Aside from the issue of making it fighting legal, I'm not sure that the concept would work in the first place, I'm afraid. Stretchy clothing works by being (at rest) smaller than the person who's wearing it. The stretchiness allows it to fit, while keeping it as close to the person's form as possible (since the stretchy material doesn't
want to be stretched).
Chain stretches differently. If you lay it out as flat sheets, chain starts
larger than the person it covers. The weight of the chain then causes it to pull together as much as it can, thus making it form fitting (to a greater or lesser extent). That is, rubber stretches
out and chain stretches
in.
Rubber rings would only actually stretch (horizontally) if the shirt wouldn't go around otherwise (or because the metal chain is stretching in harder). As a result, I don't think it would really do much unless the shirt were very carefully tailored, since the rubber parts would have to be smaller than the wearer while the metal parts would have to be larger. Since the two would be woven together, it'd be rather tricky to say the least.
It seems like you might have better luck blending together different directions and weaves of chain with different stretching profiles to tailor the shape and weight load more attractively. You might want to check out the forums on
the ring lord if you haven't already, there are a lot of people there with lots of experience with "costume" chain that might be relevant, as well as information on dozens of specialized weaves.
Not that any shaping or odd stretching is always necessary in any case. Because chain stretches so strangely it seems much more dependant on shape than, say, spandex, but on the right women plain 'ol 16ga 4-in-1 is * hot... .
Good luck, anyway. Hope that makes any sense at all.