Use os métodos RAMCategory.getSubCategories() e RAMCategory.getSubCategory(String subCategoryName) para buscar todas as subcategorias de dentro de uma categoria.
//Get all sub categories for a category
RAMSubCategory[] subCategories = (RAMSubCategory[])modelCategory.getSubCategories();
//Get a sub category by name
RAMSubCategory foreignSubCategory = (RAMSubCategory)modelCategory.getSubCategory("Foreign");
//Get a sub category given a path to from the category
RAMSubCategory camrySubCategory = (RAMSubCategory)modelCategory.getSubCategory("Foreign/Toyota/Camry");
//Get a sub category given a path from a sub category
RAMSubCategory accordSubCategory = (RAMSubCategory)foreignSubCategory.getSubCategory("Honda/Accord");