Login here:
NFHS | National Federation of State High School Associations if you have a login or pay the $20 and create a login.
Navigation to the rulebooks can be confusing but you start with Publications Library and go to rules information and then you will see available subcategories and baseball will be there. I could not paste that link.
The rule book and casebook can be downloaded to your computer but you can't copy and paste anything from them.