Many current gun shops send their work out as they don't do enough to offset the expense of the chemicals and maintenance involved in having a bluing operation. In 2019 Maryland, I can't imagine the hoops you have to jump through regarding ventilation, permits for the chemicals, decontamination station etc. that the State will require.
Atlantic Guns used to do it , They did a excellent job back when Scott , Of Scott's Gunsmithing wored there till he started his shop , I think that they send it out now but they do Cerakote in house . Give Scotts Gunsmithing a call if he does it I'm sure it will be a long wait till he has enough guns needing it to be worth firing up the tanks , or he may just send it out .
The shop mentioned in the "Anyone local who can tune up an old Superposed?" thread, "Midwest Gun Works", does hot bluing on rifles, shotguns & pistols. Their web site lists a cost of $120, which seems reasonable, add in another $100 for shipping.
Duffys, I had a shotgun hot blued by them a few months ago and they did a great job. I was concerned about the solder joint on the double barrel and they were able to get it done with no problems. Did all the parts of the gun including prep work. A bit pricey and took about 3 months wait time as they need to have enough work to run the blueing process.