Lol so you expect drug dealers to come post on here, 'me me I do please add me to your bitcointalk survey?'

I know a couple of people that may or may not hold some of their funds in btc, but then I may or may not know others who hold even more in fiat and precious metals.

Your best place to find them is checking every darknet site and counting them or asking them the questions you want (not in public) haha. You have more chance at getting an idea that way. Not that it matters to anyone other than the obvious.