The question of where to buy the cards generally falls on to preference, price or promotion. Buying cards can be done at all your typical places you shop (online/in-person). Cards bought in person have the benefit of knowing exactly what you’re buying. Cards bought online are often cheaper but run the risk of being mislead or having to deal with transit issues. When chasing price be sure where your buying from is approved or recommended. When promotions are available, see what conditions need to be met. After you find a place your happy with, you will probably use them for all your basic needs.