If you are trying to add a new Google Calendar to Appointment Reminder and some Google Calendars aren't showing it's probably because the Google account you added to Appointment Reminder doesn't have access to those calendars. You might run several different google accounts.
You can do one of the following:
Go to Settings > Manage Users and add a new user with a unique email address. Log out of Appointment Reminder and log back in again with the new user you created. Go back to Settings > Add Calendar > Google Calendar you will be prompted to authenticate with Google again. You can choose a different google account which does have access to the calendar you want to integrate with Appointment Reminder.
Share the calendar withthe current Google Account you added to Appointment Reminder.