Is it possible to find the AR-CL in the game instead of buying it? Or do I need to buy the weapon in order to own it?
Once you find the weapon and get it, it starts to show up in your inventory when you are at the weapon shop.
If you are equipped with the weapon, it shows "Equipped". If you are not equipped with the weapon, it shows "Owned".
The best way to find the AR-CL is by killing snipers and getting their weapon.