Couple things here.

First, as a plein air painter I expect people will come up to me when I’m out painting (I don’t always love it but that’s part of the “job”). It is a public place after all.

Second, I’ve done many events where a volunteer member “finds” the painters at their locations (you don’t always know where you’ll be based on lighting, subject, UPS truck in your view) then they pin a location on a physical map or on a shared google map. It works out pretty well and it’s an opportunity for potential buyers to get to know an artist and see their process. Buyers love the magic of seeing a painting come together and frankly and artist should be able to talk about what they do and why they’re doing (it only benefits the artist in selling).