Mauser06,
Try using the epoxy like you said but use a buffing wheel on a motor. I use it to polish claws from cougars & bears.....I don' t see why it wouldn' t work on spurs as well. If you don' t have one call a local taxidermist to see if he' d polish it for you chances are he will not charge you to do it, they usually do it as a favor for repeat business.