So I got an email from Centerfire Systems a week or so ago and couldn't pass up a MAC - 10 variant for $300. So its arriving tomorrow and I was looking around to load up on some spare mags but I'm having a little trouble finding a good supply of reasonably priced mags. I bought a Velocity Firearms VMAC-45. Their sight says they take modified M3 Grease Gun mags. Does anyone have any suggestions?