Don't use anything toxic on your buds. You are so close to the finish line, just wait it out. You can add more fans and put them on the strongest setting you can, without hurting your plants. That will keep the spider mites from mating. If its really bad there might be something natural to spray on them. But its so close to the end im not sure. A couple years ago i bought some natural, I think it was neem oil. It was in the beginning of flower though.