The last time I visited, these guys were carrying herbs...call ahead, see if they have what you're looking for. They're more/less in your direction between work and home

Here is a link that might be useful: Distinctive Gardens

For a huge selection of herbs and other perennials and very low prices, visit Black Creek Nursery. Last time I was there it was open from 8 am to 8 pm Monday thru Friday and closed at 5 pm on Saturday.

From PA 23 (near Shady Maple) go north on PA 625 another 3.7 miles and turn right on Black Creek Road and go .4 miles.

While you are in the area you might as well have lunch at Shady Maple. If you are interested in an Amish landscape nursery, visit Conestoga Nursery. It is located on PA 625 1.5 miles north of PA 23 (near Shady Maple). It is closed Tuesday & Sunday and is open from April to November

Herb Society of America's Chester county chapter holds a herb sale at Yellow Springs Inn every year in May. You can buy a a wide variety of herbs, native plants, roses and other gardeing supplies there. The variety, price and quality of all the herbs is way better than big-box stores!

Here is their link.

http://www.herbsociety.org/cms_unit.php?order_by=UNIT&unit_id=50

Have you tried waterloo in Exton. I haven't been in years but they had a decent selection the last time I was there.