WTB-Garmin GPS 180/230MAP G card GUS591SL

I have a G card for Lake MI I received in a unit I bought. I inadvertently purchased the incorrect one in a M card format.  What I really need is a GUS591SL  to buy outright or work a deal for either of the other 2 cards.(1 lake MI G card and the other Lake Erie M card- Bluechart? )