The federal government forcing a state to enforce a federal statute would definitely violate the 10th Amendment if the state has laws against that. I think most states have building codes irrespective of copyright status.

However, the very scenario is covered generally by statute already. Regulations, even copyrighted ones adopted by an agency, must be publicly accessible to have the force of law. Freely accessible in most cases relate to having physical access to the text in some free way. This seems like something that can be solved very simply on the state level: just redefine publicly accessible to publicly accessible on the internet.