Hi Simon. Figured it out.. if you go here http://users.airboxaero.com/Subscriptions.aspx Then you can get a subscription with the 15% discount applied using PARA1 discount code.
If you start on the actual Airbox site and navigate through it to the products page to buy charts...
http://www.airspaceaware.com/gps-navigation/products/
...you end up in a different web site where you can also buy and download charts. The charts are for the Aware
unit, not the Runway HD App.
Confusing to say the least and if they really want to get these products out there then they need to tidy up how to buy charts for the iPad app versus buying chart for the Aware unit.
Most importantly the PARA1 discount does work as stated by Simon..so go get the maps folks!