Hi Neuri i have this information that might help. This is just from my researching.

Merck make monovalent mumps and monovalent measles. (That is, seperate injections)
Monovalent mumps is called Mumpsvax
Monovalent Measles is called Attenuvax

Perhaps if you contacted Merck yourself to see who they supply to in Australia, then phone the supplier and find a local-ish Dr who uses them and then you have done all the running around, you just need to present to the info the the GP and they can order them. You could also ask Merk if it is possible for your GP to order directly through them.

HEre are some contact details for Merck Australia, if you have no luck there you can find contact details for Merck USA by searching.
Tel: (02) 9795 9500
Toll free number: 1800 023 135
Medical Information Toll free number: 1800 645 712

Not sure if any of this will help, but certainly worth a shot. Let us know how you get on.