Well I have 1 in good condition for sale, I was going to put it on Ebay?
The only one on ebay I can see suitable for your Bis is £95, but for £100 you can have my second hand exhaust box(only 2 years old and covered 2000 miles), a good working alternator(marelli type), a starter motor for refurb(zelmot type) and other bits and pieces(switches/jack/relays).