The first thing you need to do is to go to a reliable photographer who does this type of work and build a portfolio. Once you have this, you can take it to model agencies. Beware of sharks though. No reputable agency will ask for money up front. If they accept you they will place you on their books and offer you work when it comes in. They will take a percentage of the fee.
Good luck. Don't let sex-starved saddos like the one above put you off. If you've got it, flaunt it.