IIRC farm co-ops, rural gas stations, bulk purchases for fleets, etc…

I can remember my grandpa, a career trucker and grease monkey, grumbling about having to use lead substitute in his 60s Ford pickup when I was very young.

We had one gas station in my town in Oklahoma that sold it right up to the deadline. I used it because both my vehicles were built for it.

Cars made before the 70s need the extra lubrication in the valves or the engines wear out much quicker. Engines made for unleaded fuel usually have valve sleeves to prevent excessive wear.