Why not try doing it yourself?
It isn´t rocket science exactly.

If you read up online you´ll soon notice there´s a few different ways to "hot blue" (which is the only manner in which to do it correctly IMO).
AFAIK all of them involves a propane burner and a pot of sorts or two.

Yes. It can absolutely be done by the novice. Just take to heart that it is ALL about the prep work done.

As you might know i do guns on a more or less pro basis and as such use three different manners in which i blue.
The most "honest" one, IMO, is also the oldest one. Which will NOT work on more modern stuff using heat treated steels.

However.
For the "ol ´uns" it hands this really really beautiful "deep sea blue" the other ways do not even come close to.



All to aware not an airgun, just posted to give an idea of results. That thing, from the onset as i got involved, the ship had sailed. For real, and as it´s my personal gun i use for CAS.. i just handed it a bath in pure salts.

Gun was made in 1864. Works as well to this day, and i use it every chance i get.
You be the judge.

(As it might get asked, stocks are for a S&W model 29 i had laying around. The ones on the gun as i got it were shot so..)