There are a few universities around the United States which offer graduate specializations in learning disabilities. Although there are not many which offer this as an option now, there likely will be in the future.
Each state has its own criteria for granting teaching credentials to those who wish to work with learning disabled students. The recent passage of the federal law known as "No Child Left Behind" has raised standards for teachers in all fields. Because of this, you should contact your state Department of Education and get a list of their requirements before you begin looking for an appropriate program.
Once you know what courses you must take in order to get the teaching license and endorsement you want, you can start looking for a college that meets your requirements.