The Koreans are supposed to be pretty good right now. I don't know if it matters which vendor (re any specific make). I assume most--if not all--o the new or recent prodution mags not claimed to be GIs are Koreans these days. Try
http://www.keepshooting.com/m1-carbi...-magazine.html or
www.cheaperthandirt.com.
Edit: I thought another web address fixed but apparently not.