Forestfarm sells Zanthoxylum americanum (Prickly Ash), Zanthoxylum piperitum (Japan Pepper)(I think they have a very few of these left), and Zanthoxylum simulans (Szechuan Pepper). Forestfarm has a very good Garden Watchdog rating.

Mail Order Natives and Nearly Native Nursery both sell Zanthoxylum clava-herculis (Hercules' Club). Both of these nurseries have an excellent Garden Watchdog rating.

Shady Oak Butterfly Farm sells Zanthoxylum fagara. They have a limited excellent Garden Watchdog rating.

You may already know, but most Zanthoxylum are dioecious (a few are monoecious or polygamous). You may want to keep that in mind and get a few of whichever variety you are wanting to grow.

Pine Ridge Gardens carries it, and I'm sure their Garden Watchdog rating is great.
Sherry

Here is a link that might be useful: Pine Ridge Gardens

The plant that Pine Ridge Gardens is selling is a Aralia spinosa (Prickly Ash or Hercules Club, same common name as a few of the plants in the Zanthoxylum genus, but not related to them). I didn't even think of this one. I've always seen it referred to as a Devil's Walking Stick. This is a perfect example of why common names shouldn't be used. The OP is probably equally likely to be referring to either plant.

But, if this is the plant Button20 is looking for, Pine Ridge Gardens should be a good source. They have an excellent Garden Watchdog rating. Forestfarm and Mail Order Natives, as well as Shooting Star Nursery (good rating), also carry this plant.

OMG thanks guys so much,(brandon7)So you think that giant swallowtails would feed on the Devils Walking stick?

I don't know. I checked the web and found a few sources that said Zanthoxylum clava-herculis is the Hercules Club for giant swallowtails and not Aralia spinosa, but then I found some that listed Aralia spinosa as a host plant for them. So, either both would be fine OR some of the sites I saw are getting their information mixed up (probably because of the identical common names). Maybe someone else on here will know.

Thanks brandon7 and everyone else for your help:)

Giant swallowtails do NOT lay eggs on Aralia spinosa - it's not a member of the citrus/Rutaceae family that they use. It grows on my property, and I don't think I've ever seen any cats at all on it.
If you click on my link to Pine Ridge Gardens and scroll down, you'll find that PRG carries Zanthoxylem clava- herculis, commonly called toothache tree, prickly ash or hercules club, which IS in the rutaceae family and giant swallowtails will use it, although it's definitely not their favorite host plant. Of the plants I have that they use, their favorite host plants are Ptelea trifoliata and my orange tree - they occasionally use my rue, but after my Zanthoxylum clava-herculis only got one egg laid on it in three years or so, I got rid of it.
Please don't order Aralia spinosa is you want giant swallowtail caterpillars - if you want a cold hardy plant that they'll use, get Ptelea trifoliata. I think PRG still carries that one, too - scroll down on my link and you can see if she's got any in stock.
Sherry

Thanks Misssherry and brandon7 for your help.

Ahh, I see why I missed that. Pine Ridge Gardens has the genus name misspelled. It's Zanthoxylum not Zanthoxylem