I hope my advice will help you.

• Become active in .gov forums.

You can find a full index of government online forums at Forums. If you have a business in a niche that is similar to these forums, you may be able to provide value by interacting on the forums.

• Create content.

Write some content about a government agency or on a governmental topic. Finding a niche topic that relates to a specific agency with a website is best.

• Provide your website as a listed resource.

Use a special query to search Google: site:.gov [your keywords] + inurl:links