It's actually a 9x12cm camera but quarter plate holders were sold for them as well in the UK and colonies, also the US. Quarter plate film.plates are the same width but shorter, and they are less common.

Plate holders are readily available on ebay, just search 9x12, I've never paid very musch for them, often they come as sets of 3 in a holder. If you're lucky you may find some with film inserts. Just beware there's not a standard fit so you need to look carefully to get the right ones.

I find that searching ebay.com/ebay.co.uk only finds some of them but as the cameras were very much more common in Germany ebay.de is far better. It's all one common Ebay database but items don't always map to other countries portals. Login details are identical regardless of which portal you use and so are saved items etc. So as it happens I'm the sole bidder on a German book I found on ebay.de, now I'm watching and waiting on ebay.co.uk where I can increase my bid if necessary and pay etc.

An big advantage of using 9x12 holders is with film inserts the film is a common EU size and easy to get while Quarter palte is part of the Ilford ULF annual run and much more expensive.

Ian