Most judging events are either at local societies or at judging centers. The schedules for judging centers can be found at the AOS website. If you happen to vacation near a judging center during an event, you may visit.
Three judges must be involved. Local societies often have one or more accredited judges as members. When a visiting speaker who is a judge is present, local societies often hold judging before a meeting. Societies often bring in judges during their annual Show. We have judges in our society, and usually hold judging events before meetings when the speaker is also a judge. We will have a judging before our January meeting. You can see our calendar
here.
Many Societies broadcast talks, so even if you can't make it often, it might be worth joining.
Contact nearby Societies and ask to be put on mailing lists. Ask whether you can attend a judging event. It would help if they know you're a member of the AOS.