You can buy at MAC stores world wide. I bought this brush about 5 years ago and because I don't use it often, it's like new! I think it sells for around $25.00. I dip the tip of the brush into the loose powder of choice and tap a couple of times then swirl along the forehead, cheeks and neck very gently.
This brush could be used for dusting body shimmer powders/bronzers all over too.
A great brush to have for blending too, if you use too much blush, for example, just blend it out with this brush and some powder.
Clean your brush about once every two weeks with cool water and some of the facial cleanser that you use. Soak in the sink basin for about 10-20 minutes. Pat dry then shake out. Let sit overnight on a clean towel.
Have fun boys and girls!!!