Need some advice for my research:

I’m doing a study on a certain demographic group that purchases bulk ice cream (big ones, gallons) in supermarkets (go figure, can’t expect the street sellers to sell by the gallons).

I’m having some problems with my sampling method to use for obtaining respondents. I initially tried to use the convenience/accidental sampling, but I’ve consulted with a professor and she mentions trying to find a much stable sampling method (random sampling, etc), but they require a sampling frame, of which I’ve tried looking around for consumer groups that would fit the description of my target respondents, but to no avail. What then would be possible sampling methods to use that is stable enough, but doesn’t require any sampling frames.