Contact Jugglez at airsoftparts.ca
Tell him what type of mag it is (i.e. TM G17, KSC G19, etc....) and that you need a new feed lip for it. He may have some on hand...might not, but he'll get it in.
You'll punch out that cross pin, pull the broken feed lip up, save the rubber boot...put the boot into the new feed lip, push it back on, get everything wiggled into place and replace the cross pin.