A couple of years ago, I talked to Ed Fowler about this. He gave me the name and number of an old gentleman who used to cut horn. The basic procedure was to cut out the pieces, boil it for about 20 minutes, clamp it in a vise between two thick boards, and let it cool and dry. Repeat as needed. If the horn does not want to bend straight with reasonable pressure (don't break it), boil for more minutes. If that don't do it, boil for 20 min. and immediately put in a preheated, 250F oven. Heat for about 10 min. and try to clamp. If that don't work, try 300F. He said you can fill the oven pan with sand and stick the scales in the sand and just bake to start with,too (without boiling). A friend of his just put them in the toaster oven to heat them. He said he had done all of these from time to time, but mostly just tried to cut out scales that he didn't have to straighten . He only got one or two pair from a set of horns, but he said where he was from, the horns were free.
Stacy