Yeh I know a handful of places in Melbourne that stock MP's, including this one on Chapel. It's best if you just bought them online...unless you're prepared to pay the triple/quadruple the asking price.
On a side note, I recently visited that random Bazaar-what's it called on Chapel as well..The one that sells all that vintage and whacky stuff? Anyway they had a really beat up G1 Sixshot with no weapons for $150 plus a few other newer Transformers, including the black Sleep mode? Convoy MP for $200. Not much there, but if you're into weird smells and crazy classic stuff, this store is pretty cool