Regardless of whether you replenish your black swallowtail host plants from the local big box store, or with natives, the same rules apply; caterpillars are voracious feeders and can decimate a plant population pretty quickly, so the hard and fast rule is to plant as much as possible.
Finding a source for native host plants can be difficult, but it is so worth it once they become established in your garden! This frees the gardener from being required to maintain exotic host plants, and is incredibly labor and money-saving. Allow the plants to go to seed, and you will have a continuous source of that particular plant. Make sure to plant them according to their growing requirements for the best chance of success.
Native host plants in the Apiaceae family for Central Florida include (Chaerophyllum tainturieri) hairyfruit chervil, (Cicuta maculata) spotted water hemlock, (Cryptotaenia canadensis) Canadian honewort, (Daucus pusillus) American wild carrot, (Eryngium aquaticum) rattlesnakemaster, (Eryngium aromaticum) fragrant eryngo, (Eryngium baldwinii) Baldwin’s eryngo, (Eryngium prostratum) creeping eryngo, (Eryngium yuccifolium) button rattlesnakemaster, (Lilaeopsis carolinensis) Carolina grasswort, (Lilaeopsis chinensis) eastern grasswort, (Ptilimnium capillaceum) mock Bishop’s weed, (Sanicula canadensis) Canadian blacksnakeroot, (Spermolepis divaricata) roughfruit scaleseed, (Spermolepis echinata) bristly scaleseed, (Tiedemannia filiformis) water cowbane, (Trepocarpus aethusae) white nymph, (Zizia aurea) golden alexanders and (Zizia trifoliate) meadow alexanders.
You can read about Mock Bishopsweed here.
I have (Ptilimnium capillaceum) mock bishopsweed seeds for sale here at my Ebay store.
 As I’ve already mentioned there are non-native host plants such as green fennel, bronze fennel, parsley, and dill, that are easily obtained from local big box stores, but if you would like to focus on native plants I would suggest joining your local chapter of the Florida Native Plant Society. Local chapters will often conduct field trips to local native plant nurseries, otherwise closed to the public, which is a great way to obtain native plants. Also, many meetings will have plant raffles, and members willing to share plants and seeds. It can be a great resource.Â
Seed exchange threads on sites like Daves Garden or Houzz’ Florida Gardening Board is also a good way to obtain seeds or cuttings.
Another good resource is your local county Extension Office. Master Gardeners will often tend a small nursery there where you can purchase native plants. You can locate your local extension office here.
Last, but not least, learn to identify Florida native plants through the use of field guides, apps, or websites.