Do you expect to get it for free ?
Used ones from me are $ 50 ( AUS )
It is a plain old full wave rectifier with a heat shield.
You can pick up one from any electronics store but you will have to work out some sort of heat dissipation system.
You are looking for a 10A or 15A one ( bigger wont matter, smaller will )
The 2 wires that go together are the alternator wires being AC does not matter which way round they are connected , the loose wire is the + return to the battery and the mounting bolt is ground.
Most motorcycle breakers will have boxes of old regulator rectifiers but you will have to work out the wire connections.
The ones from the trail bikes tend to be simplier.
They are relatively expensive because they very rarely go bad so sit on the warehouse shelf for decades acruing warehousing costs & interest on the manufacturing costs.