Cartech (also called IDB I think) in Richmond (right by North Richmond train station) was used by a friend and he said they were reasonable and good. I have spoken to them and it seems to be run by an older guy who isn't interested in bullshit.
I've heard varying stories about some of their work, but as an engineering place they seem ok.
You can also get a list of registered engineers from Vicroads and give them all a call.