Have a look on Pembrokeshire Classics. They have an M21 with Watsonian/Squire sidecar. I rang them up but they wouldn't sell the bike on it's own and I didn't want the sidecar (well they would sell the bike on its own but at the same price!!). You need to talk to the father as the son who is the mechanic couldn't even tell me if the bike was factory numbers. It also seems expensive for what is basically a non-running "box of bits" but it did appear to be complete