Buying fireworks at some specific and random dates could be incredible hard to get. In most places locating a store that has them available all year round is almost impossible. But you can buy them online.
Amazon has over 100k results for fireworks, yes! You can buy a lot of them from Amazon. You can buy snappers by the dozen, or Uncle Milton Grand Finale with a switch to turn them on, or even small sky lanterns.
Smoke balls, firecrackers, anything you wish for, you can buy your explosives from Amazon. There are even rockets with launch sets available from the best store online.