Your best bet would be to reach out to Ga Precision or Mac Bros. Because it has a breach ring with tight tolerance like the Badger M2013 you can order pre-fits but you will likely have to send it out to a smith to have it measured before you can order off the shelf. Patriot Valley, Bugholes, 5x5 Precision can do that as well.
I can't make a "sight unseen" prefit for a Tempest.
I can fit a barrel to the action and then when it comes back we provide the owner with a lasered tag with all the critical dimension on it. This way we only need to see it once.
Not as easy as a straight prefit but sending the action up to Josh and having him do that first barrel will allow you to just order barrels from him in the future just like a prefit. I did that with my Surgeon. He got the measurements and any other barrel I needed, doesn't matter caliber, he can just spin it up and send it to you.