You can not "Blue" a stainless barrel.. bluing is a controlled rusting process.. stainless will not rust.
THAT SAID, you can duracoat, ceracoat, or flat spray paint your barrel.. or you can have it hydroprinted, one of our sponsors here does that NW Hydroprint.
Or you can have the stainless bead blasted to dull the finish so it is a matte instead of a shiny finish.