The best place to meet them is at educational events that attract a lot of people and network with the people there who are doing deals — such as REMentor events (I do teaching for them, I must confess). The other people in the room may be Sophisticated simply by virtue of having been trained by the people who are hosting the event.
People on crowdfunding platforms can only accept Accredited Investors, so that’s probably not the best place to look if you are wanting to meet sponsors who can accept non-accredited investors. Crowdfunding events are really geared toward sponsors and services related to crowdfunded (Rule 506(c) or Regulation A+ offerings), so they are likely not the best place to meet 506(b) sponsors either.
Or you can ask Securities Attorneys for referrals to their clients who are doing such deals. Most of my clients do Regulation D, Rule 506(b) Offerings until they run out of Sophisticated Investors. By then, they have typically generated a sufficient track record that they can successfully crowdfund an advertised offering under Regulation D, Rule 506(c).