I would personally be curious to know if there even <i>is</i> a company that's associated with pinball legs in the way that, say, Mirco is for playfields.
Unlike things like playfields that require specialized techniques, pinball legs are a pretty straightforward job for any company that does metal part manufacturing. And they're virtually unchanged from game to game. So if you're a manufacturer like Stern, you can probably just say "Here's our specs, we want 10000 sets of four", and send the proposal out to lots of companies for bids.