Yewsage,
Try googling "Boone Trading Company."
They have both gemsbuck, and water buffalo horn for sale.
Thomas Duvernay has a DVD on horn bow making, and there is another one "Building the Asiatic Composite bow" that shows a lot of the steps in the process.
Lived most of my days in the East Kootenays till lack of work sent me to Alberta.
Sure miss the mountains.
Best of luck with your project!
RW