Personally I wouldn't bother.
This is a pretty rare and undesirable option. DRB didn't make many crown-based kits, before changing to their own space frame chassis.
Also a crown based kit, even if you can get it approved/reg'd, will have a lot lower resale than a space frame kit.
The only advantage I can see, is if you can get it registered as a Toyota Crown rebody. That should mean that you only have to comply with ADR's(emissions etc) that were relevent to age of that crown chassis. I really have no idea, but it might be possible.
Best bang for buck will be an older DRB or RMC, partly completed. DRB changed from narrower guard body shape to wider 427 body shape in 1995, so watch out. DRB would be much more common than RMC and cheaper and easier to build...but probably not worth much as same conditon RMC. DRB have a stigma(torana based). I think all of kits have advantages and disadvantages and I personally quite like DRB's. I've built both DRB & Harrison.
Actually an RMC should be more common in WA, that's their home. And also where a lot of windscreens come from.
First thing I would do is contact engineer. Try a few and get one that is enthusiastic about Cobras. Then get current rules and regulations for WA.
Then I would start researching what parts cost etc. Especially body chrome stuff, if they are included with kit, makes it worth much more. For example, windscreen is worth $1450 last I checked. Then look at quality of job, wiring is a real good yardstick to use if it's there. Is neat, did they use lots of colours, does it look like a quality job. It's hard to hide dodgey wiring.
Too much to list here as to what else to look for. I really think you will have to widen your search to include the East Coast. You can always ask for club members to inspect a car for you.
Posting here is a good start.