Well this is a webpage where you can pimp your old school consoles.
Website: https://www.retromodding.com/
Well basically they sell replacements for you old school controllers some everydrives and also the link cable for the gameboy advance that cool.
Also if you love your old school gameboy color and game boy advance you can buy a light screen.
So you can finally see in the dark your game boy
Now what I most recommend of this webpage is the rechargable battery. this will save you alot of money on batteries if you still into gameboy advance you must check it out.