Nick,
What you are going to want to do is take a look at the schematics of the card engine and also get the LH79520 User Guide from Sharp. All of the available GPIO signals will be found in that guide. You can than find which ones you can use versus which you can't because you are using a peripheral.
LH79520 System-on-Chip User's Guide
http://www.sharpsma.com/part.php?PartID=173
Chapter 8 - I/O Control and Multiplexing