If it's nickel, it's a Combat Master Mk. II; if it's stainless it's a Mk. V. Mk. V's appear to be the most common of all Combat Masters, as I've seen more of them than all others combined. I see original mags at gun shows, and they are usually priced at $40-$50. Metalform makes a Detonics mag, and they can be bought from Brownells, or possibly straight from Metalform. Officers ACP mags will work, but they hang below the butt, as do Wilson mags for their Sentinel; you might as well use full-length 7-rounders if they're going to hang out. I use Metalform 7-rounders as spares, and try not to drop the original Detonics mag any more than necessary. Prices for good "shooting" examples of the Mk. V range from $500 to over $700. All-original guns with the factory accessories - pouch, manual, sight adjusting wrench - will bring the most.