Based on my observation a lot of people doing this, When they get arrested and to get their weapons back they simply join Police force to buy weapon where they save a lot of money thus they have access to the weapons that haven't reached the level to unlock it.
For my suggestion I want that the weapon you buy from the cop shop will disappeared if you go off-duty then if you go on-duty It will appear again it's also good to avoid the abuse.
In order to have their weapon back they simply must go at the Ammunation to buy one.