There is a place in Tolga who is quite good, but when I originally looked at this project a while ago I went in and asked him then about ply and he said nothing cloes close to the weight of form ply. Here is a link to my Orpheus Silex project viewtopic.php?f=18&t=59173 I was planning a simple plinth like this, but more square of course and with an arm board maybe. My Commonwealth does not have an arm board the arm mounts directly to the plinth, I am wondering about maybe fitting some kind of isolation washer under the arm board. The Orpheus sounds great, but the plinth is really not very heavy at all so I wanted a much more heavy and dense ply this time.bra10n wrote:Personally if I was looking for a straight forward build I'd be using the Hoop Pine with an A/C face from the link I posted above or similar. Ultimately the decision is yours but as the plinth will be veneered I think you'll appreciate the flat and stable substrate when you reach that stage. From memory 9mm thickness is a 7 ply, 12mm 9 ply.
I have no affiliation with the company but I have used them before and I know as a wholesaler they are 'distributor' orientated... just how near to you is the question. Otherwise search out Austral Plywood distributors in the far north.
Edit: Noticed your question on the arm board...
Not sure what design you favour but ply would allow you to customise each plywood layer as you're building the plinth leaving you with something like a drop-in panel that can be fixed with screws...
If you were buying flitch (veneer) you might also consider buying an additional matched leaf section from which to cut the veneer from for the arm board so it grain matches when assembled.