I once tried to track down the original source of NeXTStep when I was working on adding NeXT black hardware support to QEMU, but had no real idea who to ask/whe

I once tried to track down the original source of NeXTStep when I was working on adding NeXT black hardware support to QEMU, but had no real idea who to ask/where to look. I know it was sold at a hefty price back in the day, but I have no idea if anyone actually purchased a copy.