From info in a thread off of PhotoNet, (below) it appears that MAC, Mamiya America,
sold much of their remaining Mamiya parts inventory to KEH, in Georgia.
180mm lenses for the RB are very common on the auction site, and
as you stated, you found another lens for far less then KEH's repair cost.
If you don't work something out with Paul, or anyone else, you
may also want to give Carol, at Flutots a call.
PS: Like many, I don't like to throw away anything, either.
From the thread at PhotoNet: http://photo.net/medium-format-photography-forum/00bMf5I asked MAC (Mamiya) if they had a part for my C220 camera and they said all parts were sold to KEH when they moved to a new location last year.
Initiate a dialogue with Carol, at Flutots.