I'm not going to be much help but there are plenty in Werribee and Hoppers.

Also there is one in Prahran and Footscray that I know of.

Over here we call them indoor play centres... well at least in the scummy western suburbs we do.

I am sure there will be more than that though, and definately some in the area you described as they are quite popular here.

Maybe if you put a post in Local members forum under Vic indoor play centres you might have some more luck. Enjoy your trip when you come over.