Consumer marine electronics in Wall NJ has them, you can search them online. I bought one from the last year and have been refering people to them for over a year, they are one of the few who still can get those chips.
Timing is everything. I shipped a boat from Baltimore to Florida last spring and it had all the Chesapeake Bay area Navionics chips. I had no use for them here so I posted them on Ebay. They all sold for about $20 each. Some people got great deals. I'd recommend checking Ebay to see if there are any more. Good luck