GB parts for sale on GB. Looks like they have lots of wear. Can't really tell if the slide is parked or blued because of the blue background, but my guess is it's parked. The mag definately looks parked.
Not my parts for sale on gunbroker for the Steyr GB, I was just giving people a heads up.
Looks like you have a Steyr model 1908, very nice! I think Triple K makes aftermarket mags, but if you want the real thing then you'll have to do some digging around on the internet.
I have a 1908/34 Austrian police in 7.65 and a Pieper model 1909 in 6.35.