Marcus Music in Gwent, Wales quote about £200 for new bellows. For a Stagi box it probably isn't economically viable to post it over to the UK and back again. Try contacting the chap in the US who sells the Stagis (you'll find his contact details on concertina.net) and see if he can help you out.
It's not too difficult a job to patch bellows with thin book-binding leather. I've done this on a few concertinas now; rescuing bellows that looked ready for the bin.
Alternatively, save up your money and buy a new anglo from Marcus Music. Superb craftsmanship for a relatively modest sum; third of the price of a Dipper box, though not THAT good.
Scott