I remember the late 60s and early 70s well. You could buy crackers once a year ( month prior to Queen's Birthday long weekend in June).
Milk bars, toy/bike shops, service stations, newsagents, even Woolworths sold fireworks. Most places sold various crackers as single packs or you could buy a mixed pack of various content. Woolies for example sold 2, 5, 10 or 20 dollar packs. This does not sound like a lot of fireworks but believe me, there was plenty there for a good night. Pinball was only 5 cents per game, a loaf of bread was 23 cents and petrol was 30 cents a gallon (about 7 cents a litre).
Most kids were sensible with matches and fireworks. There were cracker mishaps but so were bike or tree climbing falls. Kids used to buy smokes for their dads (no need for ID) and we were a tough and sensible generation.
The worst part of cracker night was the smoke from the bonfires combined with the late night/early morning fog. We were coming home early one morning from our cousin's place and dad had to drive real slow as the smog was so thick.