Aftermarket in my opinion. Unknown maker to me.
I wondered that too. Strangely this is the second one that I've owned, in the last few years, the first was marked .32 Cal over Colt. I also wondered if Numrich or Sarco might have sold aftermarket mags at some point.Although what Triple K markets today leaves a lot to be desired, the Triple K brand has been around for quite some time and made aftermarket magazines as well as other gun stuff years ago. So there is a possibility that it might be a vintage Triple K magazine.