Back when I was clowning, I offered glitter tattoos as one of my services. I really enjoyed doing them because the results are so stunning and there is such a wide variety of designs. I haven’t bought any supplies in a while, but I used to get my stencils from Faketoos. They have a good variety and they’re good quality.
You can buy the glitter from several different sources, but make sure it is cosmetic-grade glitter. The craft variety is not appropriate for applying to the body, since it can scratch a child’s eye if it gets in there. Cosmetic-grade glitter kits can be bought from Silly Farm or Amerikan Body Art. I’ve ordered from both.
If you want to do glitter tattoos for an event, it’s more economical to order your own supplies and train a few people, rather than hiring it out. Training can happen in a couple of hours and you don’t need any special art skills.
To see how to apply a glitter tattoo, check out this tutorial. You can either apply the glitter with a puffer bottle, or a brush. I generally use a brush.