No, it's not a club. The database is Byron's (HK1837) personal baby as part of his book research. There's no "access" but if you post the car details or send him a message he'll give you the info required.

As for that ad, it has all the usual try hard indications, so it's possible he's overpriced, doesn't want to sell, or it's not quite as good as it looks. If you're keen on it though, give him a call. I find it only takes about 15 seconds on the phone to determine whether its a genuine seller who's simply sick of wanker buyers , or if the seller is the wanker.
You never know, he may have a very reasonable price on it and is trying to find a buyer who really wants a Sandman and will look after his baby, rather than someone looking for a quick flip to make a few bucks.
Gotta be honest, I've scared away buyers intentionally just cause I didn't like them. I've also bought things that weren't actually for sale purely because the old guy liked the fact that I wasn't pushy and trying to bullshit him.