Neil,
I'm going to post here instead of sending you an e-mail, because there might be some others that would be interested too.
I have flattened water buffalo horn, goat and sheep horn. what I did was build a simple hand press useing a 4 ton hydraulic jack.Its just a jack that has a 4"x6"x1/4" steel plate on top that raises into another stationary plate the same size. Anyway I first cut the horns in half leaveing curled halves about 5" long, then with a hot plate I heat the horn in cooking oil to around 225 degrees and leave it for approx. 10 minutes. Then working fairly quickly slide a piece in between the press plates and squeeze. leave in the press until cool, about 15 minutes and then press another. From there I drop the scale into a gal. jar with minn wax wood hardener in it, pull a vacuum and stabilize.
Good Luck
Bill