The stock Toyko Marui unit is a 2-piece unit. The JG hopup is a copy of the TM. If you're looking to replace your broken part, this is what you need to get - the TM replacement part.
The ones you're finding are 1-piece metal. These are necessary for metal bodies. I believe you can install it into a plastic body too. I've never done this myself, so please someone correct me if I'm wrong here. If you install once of these, I think all that needs to be done it to remove the bottom of the stock 2-piece hopup unit from inside your gun's body right now.
Ideally, if what I said above does indeed work on plastic guns, then that would be the better option, as metal will be much more durable than plastic.