I suppose we could begin here on APUG with a posting asking anyone with 6.5x9, 9x12 and larger versions of similar German / European cameras to send details of the film holders and cameras.

The shheer number of manufacturers of the metal folding 9x12 cameras will make it difficult, there's well over 30+, then there's the wooden (often tropical) and other cameras taking similar 9x12 or Quarter plate holders. I guess you'd have to stick to the metal holders as each manufacturer making wooden book-form holders made them to fit specific models and sometimes individual cameras.

We'd need to know edge types and overal dimensions of the holders and what cameras they will fit - in terms of what camera they where made for and also what rival cameras they can be used with.