I own two Sigmas - one in 9mm and one in .40 cal. I've had the best luck at finding hi-cap mags at gun shows.
Well, this guys gun seems fine. Ive heard nothing but bad reports about them aside from one good review at www.gunblast.com
Ive found more of them for sale, but a lot of em are 10 rounders...which is fine for practice. He's going to get four high caps and four ten rounders for range practice and spares.