I bought a couple from gunclips. They seem to be the same mags you can find on ebay, only for half the price.
I did have to do a little work on them. The mag lips were razor sharp. A fine ceramic stone fixed that. I also installed extra power mag springs as the originals couldnt keep up with the slide velocity of the Combat Master.
If you can find (and afford) factory mags they're the better choice, but these are better than nothing.