My guess would also be SMCKA, Carl would be the only place in Aus that'd possibly have a new one, but I think your chances are low.
 
There was someone else around a couple of years ago that was trying to be an Australian agent for Magnum Panels, but I don't think it ever got off the ground.
 
If you had a few spare $$, the cost of getting 2 shipped from the uk is probably the same as for 1.
Get 2 and sell the other locally to offset your costs?
 

Do you really need all the panel or just the back half ? Just thinking cause of the back of only needed, track a 4dr down as it's the same to the arch, just depends on how good your panel guys can splice in the panel .
I don't know how bad the dent is but could the crash shop unpick it and attempt to straighten it out which is easier than doing it on the car , also cut out the bad crinkles and weld in new sheet.. suppose that lot will cost up near a new quarter anyways in labour, I'll be quite now lol..

If I came across that damage, I be having a go at replicating it. A good panel beater, not replacer should be able to remake that part and doubt it'll be as costly as a full size skin..
I can remember doing a similar piece on my own mk2 coup due to rust some 25yrs ago and it's held up fine ever since.
Just my observation and interpretation of the damage.

Good call and fully understand . If their repairs are real good it's an option if no panel becomes available.
I used to have a genuine rear quarter but left hand side, sold it to my boss for $200 about 25yrs ago. Can't believe how prices has exploded since then.

Please make it be a panelvan

ok, what's the budget we can spend?
And something close to Melbourne is prob a good idea i'm guessing.
 
 
A van would be the cheapest your likely to buy in at I reckon, but they are going up also.
There was a basic neat Pinto example that sold within a day for $17k last week.
You'll certainly have some rust to play with in a van.
 
Marty was right when he warned me about the sills, floors, pillars etc, but they are basic shapes to replicate. 
 

That'll be fun to ship to you, and suppose the guy wouldn't have saved it if it was damaged.
A shot in the grit blast booth it'll come up fine, expect rust of some sort at the vent and tank well.
Get on the phone and ask about it's cond, cut the back from it and ship it home , good find !

$650 plus a couple of hundred to ship, so maybe closer to $1K?
Time and cost to unpick it, add any  local repair, and you end up with a 40 year old panel back on the car.
 
I think it's borderline for me.
 I get the impression you are doing the car up to a pretty high quality, and since you are paying for the repairs to be done, I'd prob go for new if you can handle the price difference. Maybe the PB can give you an idea in the time he'd allow for the repair vs replacement to help you decide?
 
I'm working in a lot lower value of end product than the RS, but I would have given it a go just cutting out and making a repair.
Someone with alot more skill would be able to do a decent repair I'd reckon.