Some of it depends on what kind of finish you are looking for or what type of horn you are making. If you have gotten through the rough work and shaping and are down to finishing scrapers may be your first step. Don't spend money on fancy scrapers as Robby said old saws may be broken and ground, you don't need any fancy shapes a straight edge will do what you want, different sizes may help. Broken Band Saw, Hacksaw blades work well. A scraper used right should flex a bit. A couple are shown in the Pix along with the small draw knife that I use to start, the one was an attempt to make a draw knife of sorts out of a utility knife blade, I didn't like the way it cut, until I took the knife edge off of it, squared it up, still doesn't get much use. I do not put a burr on the edge but prefer them square, done by rubbing them flat on a stone, all flats including the edges, just keep them square to the stone. A block of wood with the blade held at the side rubbed back and forth on the stone works well for the edges. Once you do all Six sides do them again. Held at an angle you should get nice shavings off the horn.
Once again depending on the style of horn scraping can be the final finish. Roughed with the draw knife, then shaped with different cut rasps (should not be able to see any cut marks, here is where a scraper come in handy, to check, coat the horn with a dark stain, wipe it off and you will be able to see any marks, use a scraper to removed all the marks and stain, this may have to be done more than once) next with sandpaper starting with 60 Grit and moving to 100, 150, 180, 200, 220 and 320 followed by 0000 Steel wool is the route I usually take.
Tim C.