I did think about adding code to a custom appointment form to do this task if its easier, but I'm still not sure how to get the name of the current calendar.
I think it would be something like Application.ActiveInspector.CurrentItem.Parent but this doesn't seem to work.
I've been using the code here:
Copy New Appointments to Another Calendar using VBA
to duplicate all new calendar appointments from my calendar to a SharePoint Calendar. What I'd like to now is to duplicate all calendar entries I create in other users shared calendars as well.