compatible wireless usb adapters

PLEASE HELP URGENT!

I am out of town and desperately need to find a " compatible wireless usb adapters" to run off my aunt's Linksys WRTG....old wireless router-she cannot remember her WPA security code? I am using a MacBook Pro running Mountain Lion.

I am currently standing at Staples Tech support desk and they are searching too but seem to not be finding anything.