Hey cool!
My family was stationed on Kadena during 75-77. I got my first Sansui 8080DB there. I also graduated from Kubasaki HS. It's been awhile since I last visited but I remember Gate 2 that goes out to Koza had a bunch of stereo/pawn shops. Also down in Naha you can find tons of audio shops. Ask the cab drivers with the pimped out rides.
With all branches of the services there and all of the bases, you maybe (most likely) will be sitting on a gold mine.
Happy hunting and welcome to AK.
Carl