Idealist is a super site dedicated to opportunities in the nonprofit sector! If you know this is the kind of work you want to do, I’d suggest subscribing to their handy email alerts about open nonprofit positions in your area. This is actually how I found my current position, doing things I love with a company I adore.
You can additionally look for internships and volunteer opportunities, as well as just read about nonprofit organizations in your area.
If you create a profile with your experience and the types of work you’re seeking, sometimes organizations will even contact you proactively!