I live in CA, is there any internships in the state for high schoolers involved in government/legal/political issues? What is the best way to research and find these internships?
Tossing in my vote for political campaigns. Internships can be pretty hard for high school students to get depending on your age but I know some friends have had good success with political campaigns. While not necessarily focused on government/legal/political you might be able to find something from these sites. https://www.internships.com/high-school/california and https://www.indeed.com/q-High-School-Intern-l-California-jobs.html
I agree with @isaac, usually campaigns or internships with your local government will be your best options. Especially with state officials (like members of your state assembly or legislature)—they'll often have space for high school interns if you reach out to them and ask.
As someone who volunteers on presidential and congressional campaigns... one thing you can do for internships is work for the campaigns. Just email around... sign up for mailing lists. For instance, if you go to (insert candidate name).com you can sign up for canvassing shifts and phone banking shifts.
Also you can intern at congressional offices. I worked at the office of a US representative this past summer and it was an enlightening experience. If you are super into politics you should go to a congressional person's webpage and ask to intern at their offices.
Hope this helps.