Hi Chuffy,
How has the thread become stripped?
It is possible to restore the thread in your BB, what is the frame made of?
One solution could be braze which can then be re-cut, there are other things out there for such purposes, including alloys which use the braze principle.
I'm a member of
www.mig-welding.co.uk, the guys on this forum are incredibly helpful and I'm quite shore would offer some very good advice, I'd suggest putting a post with pictures onto the forum and seeing what the responce is.
I don't think that the BB shell needs to be replaced, have you asked a frame builder about thread restoration? Probably a safer bet than the LBS anyway.
Steve