For black manganese parkerizing kits try:
http://shootersolutions.com/higdenchargr.html

But it'll be more agonizing than taking a can of spray paint to it - you really should sandblast or bead blast before parkerizing.

Duplicolor makes a series of engine spray enamels that are perfect for guns - enough heat resistance for barrels but much more durable than the very high temp paints that need an oven cure. And a lot cheaper and easier to apply than Dura Coat or similar dedicated gun paints. You can get a low gloss black Duplicolor engine enamel that may look like what you want in most auto parts stores.