The only ones seen in canon belonged to Sirius and James, but they're so tactically useful that of course all MoR aurors have them. This somewhat implies that they aren't exactly easy to come by, but doesn't make it clear if this is because they're too costly to make and mass produce, if they're strictly regulated, or if the Marauders were supposed to have developed them. (Even if the marauders developed them, you'd think they would have shared the secret with the Order of the Phoenix in the first war, so I doubt that's the explanation. They're probably just difficult to produce on mass, either because the process requires a highly skilled wizard, or because the wizarding world can't seem to mass-produce anything but candies and newspapers.)