you need to have a premium domain too like city.com or something. and put really good information on it like some sites with authority
Research what pages are linked from particular .gov sites you are interested in, and you can brainstorm some tactics after.
It's pretty hard, and a lot of effort, I haven't managed to do it - even if your site is relevant to a niche, and does add value, and is used by an educational resource there are so many approval flows to go through the effort level is insane.