steam wallet

Hello , i have a 20$ gamestop gift card ( 10$x2) and i was looking to buy a 20$ steam wallet but i couldnt buy it online and there is no store in my city ! is there a way i can trade my gamestop wallet into a steam wallet , any help please ! edit : or can someone working at gamestop or a staff get me a steam wallet and i pay him with the gamestop wallet??