Your antelope mount shouldn't smell at all, when you get it back, if done properly. We have them in smaller offices and bedrooms in the house and have never had an odor. Did your taxidermist possibly use a wet tan process? That has a very distinct chemical odor, even after drying and may take several months to fade.
Once the thing is caped and all flesh removed, ears turned and lips split it will be tanned into regular leather and there will be no smell. Was the cape properly taken care of prior to giving to the taxidermist and not spoiled? Laying up the mount and using killer hide paste might add a little, but is gone as soon as it dries.
We take the horn sheaths off using the microwave method to warm them up, then clean with lacquer thinner to de-grease and kill any parasites on the outer portion, and let dry. Scrape the horn cores and skull plate completly and let it dry for a day also. Bondo the sheaths back on and there will be no odor at all.
If it persists, you may have to use a strong air freshener or have inherited a "garage mount".