Find a local plating shop; if they’re worth a damn, they should be able to easily do it for you.
Don’t know where you are here in Texas, but I just found a good anodizing shop down on the SE side of San Antonio…. They’re doing an upper receiver and a hand guard in ODG to match my current rifle, and the Geissele ODG scope mount I scored last weekend:
Wright Metal Finishing LLC
106 WILDWOOD RANCH RD, Adkins, TX 78101, US
(210) 355-4186
[email protected]
Also gonna have them anodize some raw titanium fasteners in matte black while I’m at it.