Other than TGS.com, Greg Cote LLC has become my go to source for Sig Sauer magazines and parts kits. His prices are reasonable, $5.95 shipping on all orders is a huge plus, and his communication, customer service and lightening fast shipping are top-notch.
I now have spare parts for all my Sigs as well as a reasonable (or at least minimum) number of mags for each gun. Then again, can you ever really have too many magazines?
Of course I only have one mag for the Bersa, which is completely unacceptable. As Tam would say, one is none and two is one.