Some where around here I have a note included with a Brownell  bluing kit that recommended fuming nitric acid. Of course by the time I got the note I no longer had access to fuming nitric acid. bummer. 
One might be able to do the same thing with nitric and sulfuric but making the mixture is touchy. LOTS of heat and a good chance of getting spattered. Nitric acid gives nice yellow stains on skin whereas Sulfuric acid itches. Don't ask me how I know. 
One of these days I need to try the nitric/hydrochloric combo.

Anyone here involved in the welding and fabrication trades ? I was and when welding stainless steels, usually by tig, when the work piece was cold, i used to use a "Pickling" paste on the parts to remove discolouration from the weld area.

One friday evening i had applied this pickling paste to a lot of parts and closed up the workshop and went home. Being left on the stainless steel for a long period of time did it no harm.  

Anyway when i came back on monday morning, everything ferrous in the workshop, had an evenly applied coating of fine rust, i had forgetfully left the cap off the pot of pickling paste. 

This paste had very strong fumes, and if splashed on the skin, turned it yellow. I think the main bulk of this paste was nitric acid. It certainly had a reputation amongst tradesmen of being nasty stuff.

It might not be ideal, but if you cannot buy nitric acid straight, it maybe a work around.

P.S. I had a look, its available in 2kg tubs and is a mixture of Nitric (25%) and Hydrofluoric (5%) acids. 

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Not this side of the Atlantic. Nitric acid is used in the manufacture of explosives, so its virtually impossible to buy by civilians. Believe me i've tried. I used to be able to buy a tiny amount off a local pharmacy, that did everything, veterinary, human, industrial chemicals, it was like something out of Hogwarts. Bottles and vials everywhere. Its an Indian take-away now