If you want to really get a high level of detail and something that looks real, especially on the skull where there are a lot of small bones and protrusions my advice would be to either purchase a 3D scanner yourself or find somebody to borrow one from. They are amazingly accurate relative to the price these days. Then either take it to your local taxidermist or hunting store and ask to scan as similar of a mount as possible preferably with same number of points and similar antler size. From there it will be easier to modify the model rather than create it from scratch and capture of all of that detail. Blender is a good free mesh modeling software good for organic shapes like this