Umm no MasterNate
The GBC can not be back-lit the same way as earlier gameboys. Don't give people faulty advice.
Watch this video for more info.
I recommend this kit for a GBC back light.
Then whats the problem? There are 3 different sellers on page 1;
http://store.kitsch-bent.com/product/custom-buttons
https://www.retromodding.com/products/gameboy-advance-buttons
https://handheldlegend.com/collections/gba-products/products/game-boy-advance-buttons