Can an individual to buy a domain name containing only the name of his country or those domains are available for registration only to the government? For example spain.com, france.net, etc.
Domains are first-come first-served. They can be revoked, however, if you're violating someone else's copyright. Names of countries aren't trademarked so if the domain is available, then you can probably register it without any concerns. The policies for country-code top-level domains may have specific provisions regarding geographical or political names, and even point-of-presence requirements, so check the terms of service for the top-level domain you're registering within for specific details.