Hi Brent,
I started a thread a month or two ago because of a similar situation. My 22 Cruiser came with a Garmin 2006c which uses the same cards as yours does, and likewise I found that Garmin no longer sells them. I was looking to either buy some cards from C-Brats who were no longer using them, and/or start a sort of "card exchange" wherein we could lend them around (since few people can boat in more than one area at a time).
The thread didn't really take off, but then too, I didn't have much to offer at the time - just the one, lonely card that came in my 2006c. Since then I have slowly found and bought a few cards, so maybe I should resurrect the thread for the "lending/exchange" function :?: (A C-Brat did PM me and offer to "burn" me a specific area I needed, which was really nice :thup)
You may already have discovered this, but I found two decent sources to be Craigslist and eBay. On eBay you can get many of the cards - albeit they are not cheap. I found myself weighing up the cost of cards vs. the cost of a new plotter that came pre-loaded with a great many of them (they seem to come pre-loaded with either coastal or inland, but that's a lot of cards to buy individually). Craigslist seems to have more reasonable prices, but is a bit more hit-or-miss as to availability. I guess a lot depends on whether one plans to "keep it local" or travel widely.
I did decide to buy cards and stick with my 2006c for now. I like the way it functions, and also none of the new ones available now just exactly suited my fancy (which, for the price, I would want them to). I figured that if/when it came time to upgrade (later), maybe there'd be a clearer choice for me for a new one.
Sunbeam
PS: What got to me as I was card shopping was just *knowing* how many people probably have unused ones gathering dust in a drawer but just haven't thought to try to sell them!