You do not need a broker in this transaction; however, a broker is highly recommended, as they will find the space for you and guide trough the whole process.
buying a deeded parking space is the same as buying a condo. Please make sure that you do have a good counsel on your side.
Best of luck
Anyone with a deeded parking space can sell you one, as long as there are no restrictions by the owner's condo association. This must be checked thoroughly before you give a deposit.
I recommend you hire an agent for this. Furthermore, you may need to add another X to your price.