Hey guys i need some help for a weapon system

hi,
i have a problem
im making a gta style game with birds view and the battle system is the same so…
the problem is if you buy a pistol and afterwards a bazooka and you want to change from pistol to bazooka(by pressing D)it goes to the next weapon thats the uzi but actually you didnt buy the uzi!
so my question is:How do you make a weapon system like in GTA?
thanks for reading
and PLZ Help
thanks