there are two ways to make sure your pig get's enough vitamin C..
you can give a cup of a fresh variety of vegetables a day, per pig. (kale, spinach, bell peppers, green leaf lettuce, romaine lettuce....) there is a list at the top of this forum stickied.
You can also give the tabs. I give mine a 1/2 of a tab, 25mg. It takes awhile for them to grab them from you, stick it in the back of their mouth so they have to chew.
I'm not so sure they'd pick the pieces out of the food if they don't want to try it.
I used to use fresh veggies daily, but it soon got to be over $50 a week when the pig count started to rise. They only get veggies once or twice a week now. Veggies are really the best way to go about making sure they get vitamin C, and they are generally well loved and begged for by the pigs!