If you are trying to slow down sales to the point that you are able to consistently replenish stock before the last batch sells out, raising the price will reduce the volume of hard bread being sold. At some point the volume should be low enough that it stops going out of stock.
Well if the goal is to never be out of stock, just keep one more packet in the back room and never sell it.
That clearly isn't the goal.
Just “having hard tack in stock” isn’t the objective to solve for, though.
I’m actually skeptical this shortage affects people too badly, since the stuff lasts forever. Probably enthusiasts have enough in their pantries to last them through a temporary factory downtime?