Have you tried scraping? Not kidding.

You can get a better finish than sandpaper with a sharp scraper. And they are easy to make and sharpen. A concave scraper would produce repeatable results quickly.

If you could grind steel, horn could easily be ground to rough shape or hand scraped in a few minutes.

I make them from cheese knives from thrift stores, (already have handles) putty knives or old cheap carbon steel knives.