If second-hand is OK, there's always eBay (search for contact proof printer or contact printer or...). Or a real-life photo fair (I believe there's one in Antwerp a few times per year, I should have a leaflet about that somewhere.... :rolleyes:
If you want it new... well, Paterson still makes them, see here, but "quantity: 4" sounds like Paterson wants us to get 4 of them in one buy. Hey, I only need one!
At least one website where I found the item is fotomayr.de (Heimlabor -> Zubehoer -> Rahmen); not sure if it's a Paterson, though. Also, when I look at the price, I'm a bit shocked, so I'm considering 2nd hand.