I was after one a while back. I ended up buying a new one from one of the European suppliers. I can't remember where from but it looks like they are still available.
The problem with these speaker panels is that the brittle plastic spigots tend to be broken. It is also hard to get the push nuts off the spigots without breaking them.
I prefer the older MDF type panels with the game specific artwork on the front. These also gave a better mounting platforms for the speakers. But seemingly Williams was deep into cost cutting by the wpc95 stage