SL1200G GAE Arm Board

If you are in the USA, then I can supply the name and contact information for a very skilled machinist with audiophile sympathies; he can make you anything you want out of metal.  But maybe I am misunderstanding your question, which seems to be about the needed thickness of the armboard.  One would assume that you own the turntable, else you would not be interested in a replacement arm board. If you own the turntable, then you are in the best position to determine the needed thickness, either by measuring the OEM arm board or extrapolating from a direct measurement thereof.  Ralph Karsten (Atma-sphere) also probably knows something about this.

All the ones an Ebay are not flush with the top of the plinth which I need for the Triplanar arm.
I am in the US.
I know I probably should just take the arm off and measure the depth since I cant get any real information but I don't want to be without being able to play music. I have the new arm in hand so I want to do it all at once.
I am working with Tri the owner of TP he just said it would take at least 4 weeks so trying to see if I can speed that up on my own.
I asked Ralph he said he needs the table shipped to him and I don't want to ship it or pay over a reasonable amount.

I would think you can take the armboard off for a quickie measurement and get it back on in less than an hour of work.  Unless you are compelled to listen to LPs 24/7, that should be an acceptable amount of down time. (I am sitting here wishing I had time to crank up my system.)
After that, you can send the needed dimensions to Colby Lamb who lives near Portland, OR.  Colby can make what you want out of any metal you want.

@lewm Thanks

OP wants someone else to disassemble their tonearm/armboard and do the work. In case someone is unsure of what he's asking.