I was using undecayed royal guard gear for awhile. A real pain to find but if you have the time they are down there somewhere. And they often don't move too far from wherever you find them. I could never actually find a royal guard claymore but the broadsword is usually under the Gerudo highlands. I occasionally found the the spear on the outskirts of the area under death mountain

I found a more consistent option was the undecayed Gerudo claymore. Pretty easy to find one or 2 near Mines under the city.