I don't know much about sheep horn. is it hollow or solid like antlers? If it's hollow, it will probably have a marrow like core which will need cleaning out before working it. Horn is composed of keratin and other proteins (like your fingernails) and can be worked by softening it by boiling:
http://www.personal.utulsa.edu/~marc-ca ... horng.html
The gist of it is....Clean out the core, boil for one and a half hours. Cut the tip off and then open the horn to gain the most useful area. This can be either a straight cut from top to bottom or a spiral cut which will give you a strip to take your buttons/toggles from.
on the subject of buttons....
I frequent a bodgers forum (green woodworkers) and the subject of making wooden round buttons came up recently. The consensus of opinion for small round wood (3/4 inch or less) is to pre drill your holes and then using a fine saw, slice your buttons off á la carrot. Or for larger buttons and using a pole lathe, rounding quartered logs and proceeding as before. Very basic but efficient.
By The Way...Welcome to the forum.
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