Then you have a freewheel (nlerner: NOT Helicomatic) for sure. If your LBS can't get cones for it, try another LBS. They're out there somewhere. Try an old Trek dealer.

I remember it seemed for some of the Maillard hubs we could only get complete axlesets (cones, axles, and all the spacers and locknuts), particularly those that had dustcaps pressed on to the cones. I think the 500 is one of those. Shouldn't cost much more than just a couple cones.