RE: Antler Mounts
If I did my own (I work at a taxy) with supplies from a hardware shop....I would use something like a 2 part apoxy or bondo. Something that dries VERY, VERY hard and then sand it down to the proper shape so the blend between the base and the bone is not visable.
Use felt as your pre-leather template, so you don't waste expensive leather if you mess up. Also, make sure on your template that you're bringing the two pieces together behind the antlers and therefore out of view when the mount is complete.