Finding an agent for your diverse book
Your agent should love your story and believe in it enough to pound the proverbial pavement to get it sold. With all the problems with the lack of diversity in published it's important you don't waste your time querying just any person.
There are hundreds of agents out there but it's important to find an agent LOOKING for diverse stories, marginalized characters, and "own voices" authors to represent. You want someone who wants you as much as you want them. Finding an agent excited about diversity will hopefully mean you'll get a champion for your characters during the negotiations with publishers. It's also important to support diversity allies because when we do, everybody wins.
That being said, don't limit yourself to querying agents who specify diverse submissions. If your story matches what an agent is looking for than that's the most important aspect. If an agent says they love space operas they could love your queer space opera even if they didn't list "queer" as one of the types of characters.
How to find literary agents who want diversity
Manuscript Wish List (MSWL) is pretty much my favorite thing. The website and the Twitter hashtag #MSWL is a good way to find agents and editors who want queries of diverse characters, plots, re-tellings....etc. Honestly the sky is the limit on what "the industry" wants and your story very well could be a close fit.
If I'm pretending to be working on my WIP but I'm actually on Twitter I like to scroll through the #MSWL hashtag and make a list of the agents hungry for diverse stories that match what I'm working on at the moment and I keep a list of them. Then I Google these folks to find their submission requirements. Pro-tip: always re-research them before you submit. What they're looking for can change or the agent can be on hiatus so reaching out could be a waste of time.
AgentQuery is an excellent free resource not just for finding an agent but also has articles on how to write a query, avoiding scams, and what to do once you've received an offer. I started with just doing the quick agent search on the homepage.
It's not the most technically advanced search function and it takes a little while to get the search terms right to find what you're looking for but you there is such a wealth of information it's worth the trial and error.
I searched "native" into the keyword search bar and it will gave me a summary list of agents. None of the summaries said anything about Native American characters in their summary profile but if you click through to the full profile you may see that they just sold a book with a Native - American main character. Now that doesn't mean they're looking for a book with my genre or plot but it at least tells me they open to Native American characters.
Directly form the horse's mouth and this case the horse is the authors themselves. If you really like a book and think yours may be similar in style, genre...etc. Find out who their agent is! There are a few ways to do this: read the acknowledgements of the book and my favorite: The Google machine! Seriously, a simple "author name + agent" will get you there.
For more information on how to choose the right agent, what to submit, and what an agent should do for you, check out: Jane Friendman