Those were built to take original Luger magazines as well as the repro stainless one provided with the pistol.
I'll give another vote for the Mec-Gar aftermarket Luger mags. I've got probably a half dozen of the mags that I use in several different Lugers of different vintage and they work well.
Seems like they are (were?) available in both blued steel and stainless.
The mag spring is heavy in them, at least for me, but they work well as I said.
The 'Mitchell Arms' marked pistol was only made for about 3 yrs starting in 91. They were made by Aimco in Houston, Tx.
Stoeger Arms bought the rights to market the pistol from Mitchell at that time. Aimco continued to actually mfg them. Stoeger, still owning the USA rights to the 'Luger' name began marking them and marketing them as such. Something Mitchell was unable to do.
Investment cast S/S parts for the most part.
I wouldn't doubt if MecGar or some other mag producer provided the magazines to them back then. A very common situation in the industry.