Can anyone advise where (in Melbourne) I can get a batch of these made up?

Any decent Signwriter should be able to help you. The easiest option is a straight our sticker, but they should be able to make them on a rigid substrate and suction cup such as the regular ones available. You will be better off looking for a smaller shop and not looking for one of the franchised stores if your after a good price

give Warb a call

http://www.esigns.com.au 

yep thats the place