Just have to keep your eyes peeled on Gunbroker and Ebay....unfortunately parts for Steyr 1912s are very hard to find just floating around on their own. Conventional springs can generally be gotten to work in most pistols but specific parts are quite rare
Over on the Jan Stills Luger side of Gunboards, there are a couple of parts guys who might have these parts.
"Lugerdoc", Jim Shaefer, "assistant", and "Aladin". Very good reputations and I've dealt with them before. No problems.