Help! 1938 B25 Competition Rear Frame (chainstay)

[daveR]

I have just started the challenge of restoring the above bike from a basket case, I have many hard to find parts missing, but my first hurdle is that I do not have a rigid rear frame (Chainstay) from the parts book part number 65-4548 (also fitted to the B26 and B24) I have searched high and low for one but with no luck, anyone have one to sell? or has anyone had anything like this manufactured? (no one including the BSOC do not have a drawing which will not help) any ideas or advice gratefully received.