Canonically, crystals were not possible to obtain in the lower levels of Aincrad.Though, it isn't said when they were available, or if players could create crystals themselves.
What's interesting I was actually thinking earlier today about why you would ever use a potion (or make one) over a crystal. And now I know why. There was a rule that everyone ignored. And in comes the rule changes. I'm fine with it. Makes the option between crystals and potions an actual option.
