I am not sure that C-Map offers these FP card format anymore. They did up until recently.
You might want to check with some of the local dealers in Maine. They might have a used one as the NN1 was very popular with the fishing fleets.
C-Map still sells new maps on the FP chip required for the NavNet 1. Navionics gave up on the NavNet one back in 2009/2012. Here is a direct link to the C-Map NT+ maps that goes on the FP chip for that machine.