After a bill becomes a law, executive agencies and independent administrative agencies issue administrative regulations and rules to implement the law. Congress can also authorize the president to make rules and regulations, a power he usually delegates to executive agencies under his control. These regulations, often referred to as "administrative law" or "bureaucratic law," are found in the Federal Register and the Code of Federal Regulations. Together these two publications contain a current compilation of all the rules and regulations which are issued by the federal agencies and the executive departments.
While it can be tempting to use Wikipedia to get an overview of a federal agency, Wikipedia is not appropriate for citing in an academic paper. The U.S. Government Manual along with actual agency web sites (see the About section on your agency web site) can give you a brief history of an agency.
Federal and state agencies may have websites devoted to popular or major legislation with information about or links to relevant regulations and rules. Be sure to check the latest update dates to ensure you are getting current information. Such sites may also offer alert services providing notification of newly proposed or passed regulations.
Laws that affect multiple agencies may have a web presence at each agency web site enumerating which regulations affect that agency's work. For example, the Affordable Care Act has its own website as well as a devoted page in the IRS website since it also affects tax regulations.
Interest groups and think tanks (.org) may also have web pages devoted to relevant laws and regulations. Be sure to become familiar with the organization's stance on the law before using its information.
Below are examples of sites devoted to laws with high-demand regulations: