GPSMap 76 MetroGuide North America

[KUppiano]

I want to add metro data to my GPSMAP 76 base map. Garmin has end-of-lifed MetroGuide North America, but City Navigator North America NT doesn't list the GPSMAP 76 as a compatible device.

My questions three:

• how incompatible is it?
• is this a technical problem, or an "unlocking/programmed obsolescence" problem?
• is there a third party map source that would provide the desired functionality?

My GPSMAP 76 is still a perfectly good instrument, and I would rather not discard it simply because Garmin marketing arbitrarily decided to EOL the device.