MrBeast enters a new domain every week so consultants are way more important to him than to a software business.
He has enough budget and fame to, as he says, use the Guinness Word Records book as a phonebook. Or any other resource that records world-famous achievements. So that's one way.
Another is to have friends in the business that can recommend people they worked with.
I'm not sure a third consistent way exists.
Edit: very good technical people can recognize very good people in very different technical fields by their thinking and communication habits. Same for business people I believe. So if you have a wonderful devops employee/consultant and need an ML consultant but have zero idea how to evaluate them, have your devops guy talk to a few candidates and ask him whether they're good technical people.