Why would I not get it from strawberries, blackberries and such? I live to far north for oranges and such, not to mention trees take years to mature for harvest. Strawberries I figure I planted a couple years ago and can just expand, blackberries people say spread easily. Broccoli might be an option, I'm not big on collard greens but they are around the area. Spinach should grow here fine. I suppose you could can that stuff as well. I usually do Peppers and tomatoes, but those don't have vitamin C I dont think.
Forgot, quash/zucchini/cucumbers grow well here.
I'll have to check what nutrition they have