every so often they do! Check the dates on them, though - some are a bit old, so reach to the very back where the goods ones are!
Another good idea that I've used: go for a walk! Really! When folks have great shows of flowers and herbs, they're outside a lot, caring for their plants. If you ask for a little cutting off of an herb, 99% of the time, they'll give it to you, along with many more.
I like to do that - I still have a geranium from a cutting I got from a lady 12 years ago. And, I've given it to many people too, since it's so unique (looks more like a hot pink mulit-petaled rose).