If you are struggling to get one here are 4 things that models can do without an agency and it involves self-promotion:
1. Try to work with a quality photographer and put together a headshot and compcard, with your marketing tools you are more likely to get a modeling agency. www.compcard.com.
2. Mail your photo to local magazines photo editors, aspiring brands and try to get some modeling experience. Sometimes experience can lead to an agency's interest.
3. Be realistic. If you think you will have it easy, be discovered, or that modeling is an easy thing to do you might as well not even try. Models are not discoverd anymore, the industry is about putting yourself out there with the right photos that best sell you. And marketing yourself to the right agencies.
If you are only 5'3" mail print modeling agencies or talent agencies. There are less short models out there but if you want to model, focus on what you do have and market that to the right agencies.
4. Try again. Just trying once doesn't always bring the results you want.