I have a Hummingbird NS25 (7 Y.O.). I do not have a c-card and am wonderning if I can find one and where. Would it be worth the investment as the NS 25 is not that accurate in finding structure. Any suggestions?

Also, what are the reviews on the Lorance i-finder H2O? Do they locate and find structure accurately? I know they have a small screen but I do not want to lay out $100 + for an new mounted GPS and fish finder.