As you said it’s because you’re a Necromancer and Kymon’s will not accept you. Only way is for you to have another character with Kymon’s who’s able to get it and put it in the transfer stash for your Necromancer - or not to choose Necromancer as a mastery until you’ve been accepted by Kymon’s, i.e. only have one mastery up to that point in the game.
There are multiple situations in this game where you are forced to choose between items. Malkadarr/Barthollem and Zantarin/Iron Maiden, the three Ravagers/Reaper of the Lost, and Inashkor/Ketan’Thunn off the top of my head. In fact, to get the three Ravager helms and the Reaper of the Lost pants, you would need 4 characters. This is a game designed around multiple playthroughs and characters, after all. I don’t see that changing.