I am attempting to maintain a fairly comprehensive calendar of theremin concerts and workshops at http://calendar.theremin30.com/. There are tools to filter events by geographic area. You can also search by keyword or artist name. The calendar will automatically shift to your local time zone, or you can manually select a different time zone.
If you have events you would like added to the calendar, contact me via the "send a message" form on the lower right side of the page.