I want to get a copy of Mountain Lion to put in Virtual PC, I went to app store, don't see it. Any ideas?

Just read and article that with Mojave which I just upgraded to two days ago, Apple, in it's great wisdom, has removed ability to get old OS. (wish I had known that week before upgrading, I probably had all old os in there)

I do see, thankfully installer, El Capitan, in my apps folder, only that one... but I wanted to try older ones: Snow Leopard to Yosemite. I think those work better with my old Dreamweaver CS3 I'll be using in Parallels.

Any idea how to get those old OS?