So there are two designs of the 18" monza wheels, Monza II's have anthracite inserts and a diamond cut face, Monza shadows are off the MK6 and have a black insert with a diamond cut face.
The original Monza II's from the MK5 were also produced by two different manufacturers Ronal and BBS the later have metal valves that are thinner than the standard rubber type.
Technically I would also consider Huffs/Detroits as Monza design 18" wheel with a different finish, but others may shoot me down for saying that.
As for reps no idea on that front, personally I wouldnt bother as unless you can see them in the flesh and pic them up in comparison to a genuine wheel you really dont know what your getting. And originals can be picked up and refurbed for reasonable money, especially if you forgo the diamond cut face!