Federal agency rules and regulations are published on business days in the Federal Register. After publication in the Federal Register, rules and regulations are codified (arranged by subject) in the Code of Federal Regulations (CFR).
The easiest method to find a rule or regulation is to locate the rule or regulation in the e-CFR. This website is current through the last two or three business days. Then use the official Federal Register or the Federal Register 2.0 to update the regulation or rule through the last two or three days.
The President of the United States also may have consitutional or statutory authority to issue documents that have legal effect. See Steven M. Barkan, Legal Research Illustrated: An Abridgement of Fundamentals of Legal Research at 247.