Hmm. There's quite a few types of plate holder, they aren't interchangeable. Try the sticky thread started by Ian Grant for some information about those.
Alternatively, how about looking on eBay.de for a camera with holders? There's a plattenkamera listing category there. A few years ago I was fortunate to buy my first 9x12 complete with a few holders, a leather case and a Rada rollback for 120 film.
If you really like that camera in the shop, get a photo of the back of the camera to post here and maybe someone will be able to figure out what holders it needs, some types are much easier to find than others.
Good luck!