I'm in sydney and i've used 2 guys who were really great .My mesa is new but they worked on my old amp and both did great jobs with a pretty messed up circuit board . both real nice guys too
One is Peach audio .David is in balmain now he used to be in coogee .he's a real busy dude and it takes a while ,like a month, but he's in demand. not sure how well he knows mesa's but I know many say he's the best valve guy around and he builds his own high end studio gear
the other is valve heaven in surry hills.Grant is another real nice dude and he has a turn around of a week ususally . I have talked to him about mesa's and he holds them in high regard so he may know them really well .
both have websites you can google