Ok I have had no problem in the proving grounds up until this point.  I have run into a door that requires a missile launcher to open.  I have found a missile pack but cannot for the life of me find the actual missile launcher.  Can anyone help!?
 
Well I can not select the missiles despite the icon being there.   My friend did the thing and got the missiles and said that was all he had to do.  I have switched controllers and everything.  I guess I got bugged.

That would mean you continued going to the west whenever you used the Friction Dampener.  Instead, you should've gone a completely separate way to the east in order to get to the Hookshot and Missile Launcher.  Here's a video to illustrate this point: