You can send the game to curators, there are tools to do so on steam for developers. You can also use keysender services, like lurkit or keymailer (I think both have free options). Do some looking around to find people that review games like your, on steam or YouTube etc, and send keys with an honest why you think they might be interested.

Costs 100 USD to put a game on steam. Don't price it too low, as it limits have much you can discount it during sales.