Hi there and welcome
You can either purchase the map as a download or as a SD card and have it sent to you.
You can get it from my link below
On that page, click on Maps, then choose North America
Then choose On the Road and you will see it as the 3rd item in the list, which you can purchase directly from there.
I can also sign onto your computer and do this for you, and accept the offer if you wish for this, else
If you need anything else, please let me know and please remember the service rating via one of the stars at the top of the screen then submit