id be surprised cos 30.0 isnt really a standard size, and shims are usually for unusual outer diams, not inner
i would think your best bet is get hold of some 0.9mm sheet metal and bodge it round somehow. kind of how ppl use a cut up can to go from 27.0 to 27.2. 0.9mm should be flexible enough and easy to cut, depends what metal you use, probably need 90-100mm long and pi30.9 minus a little bit for the clamp, 95mm?
something like this
http://www.ebay.co.uk/sch/i.html?_from= ... 0&_sacat=0
but bare in mind ive never done that so if it doesnt work dont sue me. hey what can go wrong?