Thanks to everyone for the quick and informative replies.
azdryheat - I had actually checked the sites you have linked, however, except for Wa, they only list milepost markers and not GPS coordinates (so it's not "pretty easy").
To the others, I am somewhat hesitant to try and download a bunch of data to my Nav as the system I have, including the radio, all runs off an SD card (and somewhat old technology) and I am not sure of its capacity. The set has no internal hard-drive. I actually bought it more for the great back-up camera/screen. I will, however, look into the phone app aspect so thanks for that suggestion.
Again, thanks to all for responding.
Marv