In three different towns, I've always been able to find a metal finishing company that will throw end bells and top plates in with their regular powder coat production runs for around $20 bucks per job. Same for anodizing aluminum top plates. They're always running black and the turnaround is just a few days.
Just walk in and ask.
One time I told the foreman that I had a brass top plate that I just couldn't get to shine after machining. He told me they'd polish it for $20. When I went to pick it up, the owner brought it out to me and asked what it was. When I told him, that it was for a hobby, he wouldn't take my money.