I picked some up at Northern Tool Supply. I understand they are for cutters used by carpet cutters. No wonder they are sharp and hold up better.
I also learned at the quilt show my arm is supposed to be lined up beside my body when I rotary cut, not moved in front of my body. Also, if blade is always held straight up and down it will last longer they say.
I am going to try this as it is supposed to help have less wear & tear on the shoulder. My shoulder is bummed up right now so mostly friends do my cutting. Maybe I can do some of it with these tips.