Many years ago we built a dragster and finished the chassis with a two-step process that was similar to gun bluing. Both steps were a liquid, wiped on, process. The result was a look similar to a gun barrel in color. And, like a gun barrel, it required occasional cleaning/wiping in areas that were touched. It was a good look but I have not seen the product kit in many years nor do I remember the product name.

Does anyone remember?

There is this. Not really a bluing though but is 2 part.

https://precisionbrand.com/faq/tool-black/

Got Mine from McMaster Carr
Look up tool blackening kits

Most of the online gun parts suppliers sell bluing kits/supplies.....

For instance...
https://www.midwayusa.com/s?us...&userItemsPerPage=48

Bluing or the black stuff Curtis posted both need to be kept oiled to prevent rust and fade...