Congrats on your new C-Dory, and welcome! :thup
I ran into the same thing with the Garmin 2006C that came with my boat :cry I checked in here but came up dry (however that was two years ago, so you may very well have better luck now). I did eventually amass a collection of the data cards though. My best source was eBay, and I also got one from Craigslist.
www.tigergps.com provided me with the best information to carry out "the hunt." First a list of which units used these particular cards, and then a list of the cards with coverage maps and part numbers. These helped immensely when searching/buying. Here is an excerpt and then a link to the chart cards listings (they no longer have any in stock, but the listings are invaluable when looking to buy used ones):
If you've got a chartplotter made before 2006, your unit accepts the older Garmin Data Card format. This includes GPSMAPs 172, 172C, 178, 178C, 182, 182C, 188, 188C, 2006, 2006C, 2010, and 2010C. Unfortunately, Garmin is no longer updating these maps; the last update was in July 2008
EDITED TO ADD: I just went to check, and sadly, tigergps now only shows the information for two chart cards, when they used to show them all. I did save a large number of them (coverage maps and card numbers), so if you are going to search and have a specific area in mind, I could send you information for that area's various chart cards.
http://www.tigergps.com/gablprdaca.html
Note that there are certain cards that are large or jumbo and have all the data of many individual cards. If you are only looking for a card or two, you may find that by buying an older/defunct unit of one of the above it has the card with it, especially if local.
Also, if searching eBay, note that if the map showing the cards range is a 3D like relief map, that is the next generation of cards (names are similar) and does not fit the 178. "Our" generation of cards present with "flat" maps that have no relief.
Sunbeam
