Used to use Panda and as i recall you could export the current data - might be your best choice by backing up that file. Have a hunt here -
http://www.pandacorner.com/PandaSystems/PandoCalendar.html
Backing up your events
To back up your events:
1 Quit PandoCalendar. It is very important that you always quit PandoCalendar before backing up the events to keep PandoCalendar from changing the data files while you are copying them.
2 Switch to the Finder. This can be done by clicking on the Finder icon in the dock (it is the first icon in the dock).
3 Open your Home folder. You can do this by choosing "Home" from the "Go" menu.
4 Open the Library folder.
5 Open the Application Support folder.
6 Find the folder PandoCalendar. This is the folder that PandoCalendar keeps the PandoCalendar.eventsDatabase file in.
7 Copy the folder PandoCalendar to another disk.
8 When the copy is completed, you can restart PandoCalendar.