To be quite honest, if you've worn out a set of bellows on a Bastari, it may be more economical for you to upgrade the whole box... Colin Dipper is probably the best repairman in the U.K. and his prices are very reasonable for the quality of the work. Having said that, the bellows will be better than the instrument, so it's a bit of a strange repair... Have you tried Chris Algar of Barleycorn Concertinas? He sold me a very nice Lachenal English system for about 400 quid, and he also does repairs, and might be able to suggest a solution.

Hope that helps, EJ