If you are in the UK-you could try;

BRANDONI GUITARS. tel:02089082323. Unit 3.6. Wembly commercial centre. East Lane. Wembley. Middlesex. They specialise in old guitar parts, customs and kits etc.

I have 2 12 strings. One used as a six. Heavy, yes, but the necks stay true even after many years of ill use. I found they have very hard frets-so last a long time. My Oldest is a 1968, my other about 1973 (they changed the necks and headstock about then) I prefer the oldest.

There is one for sale in the music room for £100.00! (A later model)

Richard-did you buy yours in Peckham or Brixton? Got mine in Brixton round the corner from the town hall.