Was pocking around on the net and found this reply from Garmin reference G-Chart discontinue, I think your best bet is ebay etc.
""We are terribly sorry about your feedback and would like to explain our
reasons that brought Garmin to make such choice.
The main reason why Garmin has decided to discontinue supplying G-Charts at
the end of 2004 is that our G-chart data vendor (Navionics) has been unable
to supply us with data in a useable and economic format for the G-Chart
compatible units since December 2001. The data vendor decided to change the
format and size of the cards. The new card sizes are incompatible with the
Garmin G-chart plotters and it is not possible to apply technical changes
such to make them compatible. As a consequence there are even some card
titles that we are actually unable to supply. For this reason none of our
G-Charts have been updated since then.
The decision to stop producing G-Charts altogether on the 31st December 2004
was made because we could not keep selling navigational data that would be
at least 3 years old. We've continued to support G-chart products for three
years after we introduced our new plotters and our own cartography. We have
new products released continuously, and new products on the horizon. At some
point, Garmin had to break away from old and out of date technology such as
G-chart is at this time.
Garmin launched the BlueChart marine cartography in July 2001 for a new
generation of plotters with additional and more advanced functionality,
which G-charts are not able to support. BlueChart cartography is our own.
After having tried the main two data vendors on the marine electronic
market, we have realized that the best way to serve the Garmin customers is
to have our own cartography. We have in this way total control on card
titles, technical changes and card sizes.
We are very sorry that you feel that we have let you down, but unfortunately
technology moves on and the function and feature now available for our
current range of plotters is far greater what found on the G-Chart range."