Taxidermists repair/replace antlers all the time. It's not that difficult to do yourself.

A friend of mine had one whitetail deer that he wanted to mount but someone before him had shot off one point.

To fix it I found a shed antler with a point that was close to the same diameter ,size, and shape of the same point on the other antler as the broken point. I then cut off the point from the shed so that when it was attached, it was the same length on both antlers. Then I drilled 5/16" hole 1" deep into the center of the broken point and the replacement point. I then epoxied a 1/4" x 2" threaded rod in the holes, being careful to keep the replacement point pointed the same as the other points on that antler.

After that epoxy dried, I filled the gap with epoxy paste, and when it hardened, I filed and sanded it to the contour of the original point. When all of that was done I took a shed antler and tried various mixes of walnut, pecan, or other wood stains to match the color of the original antler. When I found the correct stain, I stained the patch, and when I returned the antlers to my friend, he had to look at a picture to verify which point had been replaced.