Beretta USA has them on their site. Tried to copy the link, but my phone wouldnt cooperate.
Actual Beretta made 92 mags have the cutout for the heel release. MecGar and other 3rd party mfgs dont. The factory mags for my 92fs work perfectly in my 92s.
Greg Cote has plenty, including aftermarkets at $20.
http://gregcotellc.com/cart/beretta...92a1-cx4-15-rd-9mm-blued-mgpb9215b-p-670.html