There's no single, definitive, publicly accessible database that tracks the exact number of Licensed Vocational Nurse (LVN) schools in the US. The number fluctuates as programs open and close. Also, the definition of "school" can vary (some are within larger colleges, others are standalone institutions).
To find the number for a specific state, you would need to contact that state's board of nursing or equivalent regulatory agency. They are the authority on approved LVN/LPN programs within their jurisdiction.