Regarding Parkerizing:
I get mine done at a local business that refurbishes / custom-grinds engine crankshafts and camshafts.
The catch is that they are set up to use REALLY coarse grit (not on the journals, though) at quite high pressure, so I go to one "big shed" to get the "gentle", fine grit blasting and oiling done and then drive briskly to the place with the big phosphate tanks. Here, they promptly hose off the excess preservative oil, whack it in a serious detergent bath, hot-rinse and then straight into the phosphate tank.
If you want a "grey-ish" finish, you need zinc added to the bath; for "black", add manganese. Talk to the phosphating chaps first.