It probably wouldn't be cost-effective to produce extra dice to sell as singles or in packs of any number. Dice aren't cheap to produce, and getting the cost down to a reasonable number would mean an enormous expenditure for a product that isn't really needed (you can always just re-roll the dice that missed in a strike, for example, if you needed more than 9 dice in your roll), and so probably wouldn't be purchased. It's a balancing act of numbers. To get the cost to produce the dice low enough that the price-point at point of sale would be appealing enough to the masses the production number would have to be exceedingly high, and thus initial cost to Arcane Wonders would be exceedingly high, and it's highly doubtful they would recoup the cost.
-nihil