You might even have one made for you out of slate, for very little money. You would have to drill it yourself, which is messy but do-able. (Lots of dust.) Otherwise, I kind of favor hard woods or a laminate of wood and metal over solid metal. But my opinion is based on no data.
Aluminum or Wood armboard for Technics SP10 Mk2
I have an SP10 MK2 with the Obsidian base. The unit is in virtually perfect condition and was used residentially only sproadically when I purchased it earlier this year. I am changing my arm and I will need a new armboard. There is a person who makes new armboards out of aircraft aluminum. I could also obtain a new armboard in wood. What do people recommend (other than replinthing or "no" plinthing)?