The best way to buy those torx ends is to get a whole set of the useable range. Often, you can get a set for not much more than just one individually. I found TSC (tractor supply co) to have the lowest prices for these little tool things.
When I do anything on brake sliders, I use a hand held make-up mirror and a light, to get a good look at the end of the slider. I once ran across one slider with a torx and the other slider on the same caliper, to have a hex end. There must be aftermarket sliders out there that do it a different way.