You can try and source a replacement from Cummings or eBay. IMO I would contact sbmar.com owned by Tony Akins, Cummings dealer. They have engineered state of the art replacement systems. Ain't gonna be cheap either way you try and go.
Similar problem w/ my '04 340DA SmartCraft 2000 screen, plus the N-S-E-W pushbuttons have frozen, so I can't change screens. Mercury Marine has a replacement, Vessel View 7, that is supposed to be 'plug and play'. Check out 'Vessel View 7' on UTube, there are a couple of articles attempting the replacement. I plan on the replacement next spring, but through a certified Merc Dealer to retain the warranty.
I have replaced the SC 2k with the SC 4...BUT only after consulting with a Seaboard Marine because it all depends on what serial numbers you have on the SC BUS. Some of the earlier serial,numbers require multiple in line components to be replaced...later versions do not. Ask to speak to Brad at Seaboard. He will guide you correctly. They have all of the required hardware plus they have an option to,go all digital and get rid of the SC all,together.