So, I was thinking of a way to open to a girl in a grocery and came up with this.
(Look for something in her cart that may be a little difficult to find or rare)
"Hey, I love XXXXX! Where did you find that? I didn't even know they sold it here!"
After that, ask her to show you exactly where its at or something along those lines. I haven't actually field tested this, but I think it's pretty slick and comes off as friendly and nonthreatening.