My experiences:

Original gray Norma ones are getting harder and harder to find fine examples of. Am down to one uncut one (once had three) that is waiting for a special lens to eventually be mounted on it.

OEM black SInar boards are the most common. I have several versions that only differed in the way that they were labeled by Sinar.

Sinar "rip-off" boards. A very few are excellent. My experience is that most are thicker than OEM Sinar boards. I have acquired a few that were unusable in that they distorted the lens board sliding tabs. I now stay away from them.

I've seen some wooden "Sinar" boards FS on eBay. They will work on a Chamonix but not on a Sinar.

I have a machinist Granite surface plate that I place all my Sinar boards on to check their flatness. Surface plate is flat and accurate to 0.0002". 5 out of 10 of the used boards that I have acquired were not "perfectly" flat but easily bent back to being flat.

Filling in unwanted bolt holes is easily done with JBWeld.

One can strip the paint off the front side of a board and then respray it with wrinkle finish black paint. Visually it works, but the paint will flake off with use. I assume that the paint on OEM Sinar boards was heat cured.