I make my own from peat moss , i take some peat moss and put in water for a few days, until it begins to rut, then i take hand fulls and rub it on, it gives a natural color to it.
The chews can be fixed with two part epoxy called sculpt all, or antler building epoxy, sold by most taxidermy suppliers, you want to fix them before you stain. Also antler stain can be bought from any supplier.

I like the pea moss because I can darkened bit by bit until I reach the desired effect.

Check suppliers at Taxidermy.net/forums