Ethnographic interviews... how to find interviewees?

As the title states, I realized I'd been going about my Research & Design process by defining the hows & whats of the solution first instead of understanding the problem of the end-user first, let alone defining what exactly the problem is that I'm trying to solve.

I've seen a lot of helpful articles guiding how to conduct such customer discovery & research interviews, but how do you go about finding people to interview in the first place?

(specifically for consumer internet btw)

Thanks!! :-)