I would suggest patience and planning, It is good to be a preexisting member.

Go around and sign up at a few spots and tell them you would like to sell some flowers and ask when a good time to bring them in is and how much they commonly purchase at a time.

This way you have built a rapport and are not showing up or driving around when there is nobody to buy with a bag of sticky stinky trouble

You could also try calling ahead as well and asking if a product purchaser is there this way you don't waste your time