Call Springfield Armory. Every year at Camp Perry they have boxes with some old, funky, rejected and blemished parts, including 1911 slides.
That said, it isn't that hard to make something. I built a pivoting fixture years ago that let me bore the inside of a bushing to match a particular barrel's OD. It then tips the bushing the correct amount to take a clean-off pass with the boring bar that allows the barrel to tip up into the locking lugs. It was just a way to avoid the traditional scraping.