re: where to get some crushed limestone?

that's about half a yard which is just over a ton. So you’re looking at 2-3 pickup truck loads.

btw, you probably want to go thicker than 1.5". that's not much at all.

For reference, 10 filled to the top 5 gallon buckets (which would break anyway) would get you about 1/3 of the way down your path.