Dont pay any fees to an agency, the fee they take should be a pecentage of your earnings.
There are several ways to get the contact of those agencies. You can get in local Newspapers, Magazines or you can make search in Google. You will get lots of Modelling websites. Btw do not forget to add place, state, country name in your search phrase.
Try and find a great photographer to do your portfolio for this. If you ve done it yourself it won t cost as much make sure you have the right outfits in your portfolio. Evening wear, Swimwear, day wear etc.,