Is there a site/agency that millionaires/billionaires use? I’m looking for something specific and can’t find it on TRYST, Slixa, etc

I’d try the ISO board here and be more specific about what you’re looking for.

the net worth of the clients of any agency?

Billionaires is a FUCK ton super rich rare air. Millionaire is nice but not so rare air these days. Since this counts assets, it doesn’t always equate to the type of spending some may think. This differs by where you live, but places like LA and NYC, if you own a house, you could very well be a millionaire and not have that much liquid money.