I tried hunting through the government website, and it lists a large number of registrars, but none of them seem to offer an easy way to sign up for one. Keep in mind the following things though:
I saw another Nigerian company for which an "exception" had been made. Overall, I think it's risky business right now, especially if you manage to snag a desirable .ng domain. I don't mean this as offensive, but it's not unimaginable in Nigeria that a few greased palms could lead to an "exception" being made for re-assigning your DNS record if you don't have local interests there to back you up.
(1) You need to have a business in Nigeria
(2) ccTLDs are subject to local laws, so be careful before basing your brand around a ccTLD name. Case in point: Bitly http://workbench.cadenhead.org/news/3503/bitly-builds-busine...