Where can I get Wormwood, tarragon, mugwort (Artemisia), etc. plants and/or seeds to grow?
Certified GKH Gardening Expert
I would recommend doing a local search for your area to find any retailers or even mail-order catalogs. Your local garden center may also be able to help. You can also check out eBay. In my experience, eBay is actually a great place to find unusual plants/seeds. Just check the feedback on the seller before you buy.
For growing information, these articles should help: https://www.gardeningknowhow.com/edible/vegetables/celery/wormwood-plant-growing-sweet-annie.htm