You can buy it at their website
http://herbes-de-provence.com/ Ordering it as not as convenient if you need it right away, but with some specialty items, both food and other things, it is more convenient and inexpensive to shop for them online or order by phone.
Here locally I don't know of any actual specialty gourmet food store, but I would try Freshmarket, as mentioned above; and Ambrosia in Lake Sumter Landing has some specialty food items, as do the Banner Mercantile stores in both town squares. You might recommend Herbs de Provence to them if they don't already carry it. Also, there is an online store that I have used a few times that might have it:
http://www.gourmetfoodstore.com
The Publix manager at the store near us (Mulberry - but they would probably all do this) has been willing to special order, and sometimes actually begin stocking, a few items that I or others have asked about.
I think that all of the businesses here are open to our input as to what items we would like to have them stock.