There are people in my department who do work in this area. I can reach out and ask them.

I think Mechanical Turk gets used a lot for survey experiments because it has a built-in compensation mechanism and there are ways to ask questions in ways that filter people into precisely what you want.

I wouldn't dismiss Facebook ads so quickly. I bet there is a way to target mobile app developers on that.

My hunch is that like survey questions, sampling methods are going to need to be tuned case-by-case and patterns extracted inductively from that. Good social scientific experiment design is very hard. Standardizing it is a noble but difficult task.