For a really black, glossy finish, black chrome is probably your best bet, but be aware that its no tougher a finish than the old bright nickle, which isn't all that durable.
You can get it here, but read the information:
http://www.apwcogan.com/
Also:
http://www.techplate.com/firearms_pl.htm
The other options are one ofthe polymer colored finishes, but I don't know how glossy they can be, most people want a matte finish.