Educational dvd's, books, cd's hunt

As we are still unaware which type of speech disability own 3.5 yr old has we are treading water anxiously just now. Weve had a couple of brain waves. Does anyone know of educational books, cd, dvd's etc specifically designed for children with speech difficulty. Jack has many books but were hoping for something a little more indepth, hopefully something designed particularly for children like Jack. Be grateful for any info. Mant thanks Leah X