Frankly speaking, I'm mostly surprised that this doesn't already exist.
It does. There's a Craiglist-type feature on Bloomberg trading info terminals. Yachts, rentals in the Hamptons, that sort of thing. You can message other people via the Bloomberg system if you see something you like.
There's a paid social network for rich conservatives. This is independent, not a Bloomberg thing. It's only $5/month, which is apparently enough to keep the noise level down.
There's a persistent rumor that there are special news sources for rich people. There are, but they're very narrow. There are lots of newsletters you can buy for $50 to $1000 a month that provide detailed coverage of obscure business subjects. If you really need to know what's going on with bulk carrier leasing, oil drilling equipment activity, or wafer fab capacity shortages, there's a newsletter for that. Offshore Alert, which covers offshore scams, is one of the more readable ones, and you can see the first few lines of each story for free. There are expensive newsletters devoted to security and terrorism, which give the illusion of inside information, but they tend to be marketing tools aimed at rich paranoids.
If you want to know what's going on in the world, read The Economist. After you've been reading it for a year, you'll have a good understanding of how the world works.