There are not always modeling agencies that bluntly say "we accept petite models," but there are commercial print modeling agencies and you should consider these when it comes to submitting to get an agent. Also the word model might mean for you to be modeling sunglasses, handbags, shoes, or even just your thumb! A lot of brands, from dish soap, to tissues need models and actors and you should open your eyes to what modeling really is.- which is so many things.
Start noticing where models are that do not involve fashion. Start noticing the ads and commercials, brochures, etc. Even Tiffany's uses a "parts" model for their current ads with The Frank Gehry Collection. The jewelry hangs from the models neck ad you can't tell her height. Modeling is many things.
What kind of model are you? And do your photos say this?