Back before the internet covens would put adverts in local newspapers when running outercourts or open events. These day most use Facebook. Most states or local areas will have at least one Facebook group related to pagans, wiccans and/or witches. Join them and start asking around for community events and covens running outercourts or training nights. Community events are great ways to meet the covens in your area face to face. Just remember that covens are under no obligation to accept you.
The best way to know if a coven is right for you is to attend their training nights. I'm currently writing an article about the warning signs when joining a coven so watch this space.