If you can't find ground matzo meal or matzo bread to grind yourself during the rest of the year, you can grind unsalted crackers or lavash (Armenian cracker bread, which can also be hard to find) in a food processor or blender. Dry bread crumbs or finely crushed melba toasts may suffice, as well.
You should be able to find cake meal online throughout the year, but you may be dismayed at the quantity you have to purchase. The good news is, stored correctly, any extra meal you have to buy should last at least until the Passover after next Passover.
If the matzo meal you find looks too coarse for a delicate soufflé, you can grind it more finely in a food processor or blender.