You'll probably find that it is almost always used in underground applications, such as sprinkler systems. The idea is that the dirt packed in around the pipe adds additional inward force, counteracting the outward force of the water pressure. I haven't checked for years, but Lowe's used to carry it in their outside garden area. NOT with the other plumbing.
I have been able to find up to 1.25" thinwall at lowes and they recently put it in it's own rack in the pipe isle. No 1.5 though.