I think you want the VESA FDMI standard. It is available, at a cost, from VESA. It might be cheaper to just buy a suitable mount than buying the standard. What information do you need that you cannot get from just looking at the back of the panel?
That is what I would do. FWIW the hole pattern is going to be a rectangle with each side some multiple of 100mm. And the holes don't have to be all that precisely located if they are a little bigger than the bolts that will go through them. The bolts are metric, M4, M5 or M6 IIRC. I don't recall the pitch. Choose a length that goes well into the threads but doesn't bottom out when tightened.
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