Highsmith outsources it.I'm not sure if Highsmith's does hot bluing or not. They may outsource it. But that's Greenfield area. Kind of east central.
About an hour west of there is Havlin's Firearm Finishing. I THINK they've done hot bluing in the past. I cannot find any current reference to it on their page right now - so I'm not sure. But it may be worth emailing him. https://www.indygunsmith.com/contact-us
I can tell you how to get what looks like hot blue.
Get a large bottle of denatured alcohol, cotton balls, Blue Wonder Gun Cleaner, and G96 bluing gel, PB Blaster Multi-purpose lubricant and some steel wool/ scotch-brite pads.
Using the steel wool and Blue Wonder, scrub all the rust and oxidation off the gun. Scrub as hard as you like it wont take off any of the blue with the steel wool.
If you want to start off 'in the white' use scotch-brite pads instead of steel wool, it will take off blue, rust and everything.
After clean, rub down with cotton balls and denatured alcohol until all the oils are off. (If the bluing wears off when touched you had oil on the metal.
With a glove, touch your oil free finger to the G96 gel and rub (at room temperature) a small area on the metal, it will instantly turn blue! Wipe off with a soft cloth immediately after application, DO NOT ALLOW TO SIT OR DRY.
Continue doing small areas and blending together (it does this automatically) until the piece is all the same color of blue.
Spray liberally with the PB Blaster muti-purpose lube and rub with the clean fingers on your hand, this will keep it from further oxidizing.
Let it rest and 'cure' for a day and re-assemble. Rub down with a good gun oil and you are done.
You can do all of a gun or part. Like those holster wear marks on the barrel? Just do this to that area and in minutes you will have a new looking muzzle!
If the metal is pitted and needs to be conditioned DO THIS BEFORE TRYING TO BLUE!
The more uniform the metal is the more uniform the blue. It takes much more time to prep the metal than to blue it.
If this isn't clear enough, let me know and I will help you further. But I kid you not, it will look like a pro did your gun.
Rule of thumb: Shotguns are the easiest, then rifles and pistols are the hardest. This it due to the proprietary formulas for the metals.
I suggest getting a cheap shotgun to practice, practice, practice...
The Blue Wonder runs about $10 a tube (use very little, like a pea sized drop), the G96 is about $14-16 a bottle, PB Blaster multi-purpose (it has to be the multi-purpose and not the penetrating oil) runs about $3 a can at Tractor Supply, and the rest of the items are whatever the hardware store thinks they can get for them. I recommend starting with the 'medium' steel wool, the fine and extra fine will cause you to tire out before the job is started.