Find Navionics Classic chart or start over?

[AKA-None]

So I've acquired a Northstar 958 for real cheap. It's like new and it's pretty darn fast and yes it's old. The saddest part is right now I don't have a map available for the upper Mississippi River which I need for the next year or so.

The question is do I keep trying to find an outdated map of the river or do I dump this plotter and look for something newer? If I do go with something newer what would be my best bet in the $500 dollar range +-

I need to integrate an AP, depth, speed and wind instruments (NEMA 0183)

And yes I doubt anyone here would have a chart of the upper Mississippi.

And no I really don't want to spend the time to reverse engineer the chart format.

Or alternately can I just use it as a display but do the actual charting on another unit and send the signal to this plotter?

Puzzled on the hard