Will, Tomball and Humble? I believe have The Arborgate Nursery and they carry more herbs than most. Also out in Katy is Nelson Watergardens and they have really great herbs. The third place I have found good selection is Plants for All Seasons. All are great at information as well.
O by the way, Nelson's Watergardens isn't actually geared toward herbs, but I have found different varieties there that I don't see at Tomball Arborgate. I just came in from outdoors and was trying to id a plant, it didn't come up last year, but my Mexico Mint Marigold is coming up this year. I grow MMMarigold, lemon thyme, peppermint, Spearmint, Mojito mint, Tuscan Blue and prostate Rosemary, (Tomball Arborgate had Hill Hardy at least once this year) Hilltop Oregano, onion chives, fern leaf dill, fennel, Italian flat leaf parsley, lemon catnip, regular catnip, African Blue basil, and trying to grow sweet basil and spicy globe basil- they aren't happy. Nelson's had a powdery mildew resistant 'Eleanor' sweet basil that is doing okay. Just an FYI edit