Some plaques have indeed survived.
As for the Gold and diamond one, it would be great to get solid confirmation but as with many things in life, that may never happen.
I don't know where Tom got his information from and as much as I would like to believe that one described as such does (or more likely, did) exist there has been no other evidence to suggest that it is correct.
As I have stated a few times, no Playboy employees that I have spoken with know of a Playboy gold plaque (including managers) but again, they could be mistaken as the memory can play tricks.
Also, as mentioned before, the Clermont one does not contain diamonds and when I spoke to the person who was responsible for making it all he would confirm is that it was a Clermont one, not a Playboy one (and that he only made 1). As he advertised in the Playtime magazine I would have thought that if there was another it would have been made by him but I suppose that is speculation (which unlike others, I don't like to do).
Let's hope that one day we will know the actual facts with no "Chinese whispers" involved but I'm not holding my breath.
I wish I'd thought of asking Mr Lownes about it when we conversed via email in 2006 but I didn't bring it up (probably because I wasn't aware of it at the time as I didn't have Tom's book yet). Mind you, he told me that he only had a few low denomination chips and didn't mention plaques at all. I'd asked him if he could remember any information about some of the chips as we didn't know as much in 2006 as we do now and he was kind enough to offer some advice on how I could market a book about UK casino history I was hoping to put together. He also pointed me in the direction of somebody else that may have been able to help but his email was not still "current" and nobody seemed to know how to contact him.
I still try to ask some of the "old timers" but they are few and far between now and most just want to share their experiences and can't remember much about the gaming items, understandable.
I'm just glad I managed to find a photo at last (albeit a bad one), here's hoping that somebody can find the one that (possibly) shows the Playboy one. The Clermont photo was in a staff magazine in 1979.