If you just want to track a few individuals... Enumerate all those who possess the data. Now look for data brokers that they deal with (as commenter korse said) and recurse. Find all the employees of every company in question. Muster a few hundred bucks or so, seems to be the market price, and there you go[0].

For research I dunno. You'd probably have to make a deal directly with one of these companies, one way or another, so I would start by talking to them.

[0] - https://www.vice.com/en/article/nepxbz/i-gave-a-bounty-hunte...