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:
(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...