I met the guy that owned it a few years ago at the Wynn poker room (my brother-in-law was playing at his table). He said he still had the Diamond Club rack, including some high denominations). He also had owned a Long Island club which he had also closed (voluntarily, unlike the Diamond Club). Andy Hughes has a business card from the Diamond Club. Very cool.
For what it's worth, the other club that inspired the NYC underground clubs in Rounders was the Mayfair, which had been around for many decades before being raided. It started life as a backgammon joint.
Michael Siskin