I've never seen this before. Maybe it's common. I was looking for a 24mm Bing and found this one. The seller has completely dismantled it and is selling each individual part seperately, right down to the jets, float pin, fuel inlet connector, etc. Seperately comes to $266.05 plus shipping!
Click this, then click 'other items' then put Bing in the search box.
http://www.ebay.com/itm/1972-ZUNDAPP-125-RICKMAN-24mm-BING-CARBURETOR-BODY-/330666593559?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item4cfd43cd17
I'd buy it, Gordon. The body is the hard part. You probably have all the other parts. I have a 24 on my Wassell. If you don't get it, I might go after it.
Lew Mayer