There are loads of agencies out there but sadly about a handful of them has folded this year because of the economical climate. From what I've heard all agencies are bombarded with e-mails and requests from make-up artists wanting to join. It's quite unlikely that even the busiest and well established agencies would take anyone on right now. If I were you I'd wait a few months until things have settled a bit and then make loads of phonecalls and set up meetings with the agencies you like. The most high profile agencies don't take on people straight away, you'd have to assist their make-up artists for a while and be a "junior" on their books so don't get dissapointed if they turn you down or ask you to assist.
Try to get hold of a copy of Le Book, you'll find all the agencies in there, it's like a yellow pages for people in the fashion/media/advertising industries. Or you can check out www.lebook.com but all agencies are not on there, still worth a look though. I don't want to slag any agencies off as all make-up artists/hairstylists/stylists have different experienses and different stories to tell. A lot of artists think that having an agent is the sollution to all problems and the best way to achieve fame and fortune but this is not the case. Agencies can be quiet too and if you're exclusive with an agency you won't be aloud to do your own jobs on the side, everything has to go through your agent. Remember that they'll take 20% off your earnings too. I find that it's great having an agent when you're super busy and double or tripple booked and they can help finding someone else for the jobs you can't do, chase up payments and ofcourse negotiate good rates for you.
All the best/Lina
I have a nagent annd to be honest there really isn't alot of work around most of the make up artists I know are doing test shoots and low cost stuff. The bigger companies are laying off staff and its becoming easier to hire the actors and ask them to do the make up themselves.
Igf you do decide to go for an agent I would keep on top of them, call once a week for a chat, ask about business etc. I have a good relationship with my agent and it means I am at the front of his mind for jobs.