I pocket carry a Kahr PM9 with the six round mag and one in the pipe. I carry the spare seven round mag in the other pocket, contained in the leather slip case that came with a $4 sharpening stone at Wally World. This keeps the mag from getting full of pocket crud, and still works well after almost two years.
While this particular leather slip case fits the Kahr 9mm mag, there might be similar cases that will also work for pocket carry. For example, prior to buying the PM9, I would sometimes carry a Kel-Tec P32, and would carry a spare mag in the off side pocket inside of a small cordura knife sheath. Honestly, if I had worn the sheath on my belt, I doubt hat anyone would have given it a second look.