I have about 4 or 5 Gamestops within 20 minutes drive from me, so I haven't had this problem. The last time I was at a Gamestop, I remember seeing a sign telling you to ask a cashier if you don't see a gift card you want or something like that. I'm sorry I didn't pay much attention to the sign, but it reminds me about something
@asgaga posted last year.
In Gamestop stores, you can: Go to gsdigital.me on your smartphone's browser > Select Gift Cards & Entertainment > select the eBay gift card > Select Amount $25-100 > Click Buy (which should generate a barcode that the cashier will scan) > Take your phone to the register to pay (and they'll email you the gift card).