The dealer lost mine (or so they thought)the mgr. replaced it and said it cost $700.00 for the two discs.. It is a Harley part number if you are buying them. I don't have my bike at home but the GPS supplement book should list where to check for upgrades. NAVTEQ I believe is the supplier, for our cars the upgrades are first one free and then $150.00.
Unfortunately, the MoCo would need to request the upgrade and if they are like some car manufacturers, they don't do them often. I would be surprised if an upgrade comes for a year or two.
As far as I know there isn't anyway provided for a large amount of memory to be stored. When I rode to Cripple Creek, I didn't use any CD's, just left the NAV CD in the radio and listened to Satellite radio when I didn't have a local station, which was most of the trip.