SL1200G GAE Arm Board

Anyone know how thick I would need to make a replacement arm board for this table.
I have a template for the design and size just do not know how thick or deep in mm.
I need one that is flush with the top of the plinth.

I have not been able to source one from any of the suppliers I could find which are
mostly overseas. I did find a guy that would make one out of wood but I would like
one out of aluminum to match the top of the table.

I have found on line mfg's of aluminum parts.