HKPARTS - HKPARTS
here is link for selector lever: https://www.hkparts.net/shop/pc/Enha...-243p18257.htm
here is link for mag release extension: https://www.hkparts.net/shop/pc/Padd...R-79p17079.htm
Note: I had to use a spring (ar15 spring) from my random parts box to fit behind the detent for the selector lever I received. I guess you could cut the one that comes in the package but I found it to be too strong to rotate the lever with ease.
Thanks! That was my first go at coating a firearm. Fortunately, there are a lot of great tutorials on youtube.