Whenever I buy a camouflage for a gun in Counter Strike: GO it isn’t in the inventory

It is simply a little bit of backstory to accompany the skin changes, nothing more than that.

If you wish to read more, look in to the text in the mission journals, for a man named Booth, there is quite a bit of talk about him in there.

What you can do is to run CS:GO, open console, then unbind said keys before you rebind them. To open console, you must enable it trough the options menu, under key bindings and advanced settings. You can also right-click CS:GO in your steam game library and select "launch options". There you must write -console. Done correctly and the console will be open when you start the game again. I recommend you do a bindtoggle [ keyname ] console to ensure you get easy access to the console at a later point.

In console, write:

unbind [ Keyname ]

Then you can rebind them using bind [ keyname ] [ command ]

The unbind part may not be needed, but it's reasonable to do so you are sure the keys are completely set to ONLY be bound the way you want.