IRS Pronouncements are published in the Internal Revenue Bulletin. They are also accessible in some research databases. Here are links to a few access points.
A revenue ruling is an official interpretation by the IRS of the Internal Revenue Code, related statutes, tax treaties, or regulations. It is the conclusion of the IRS on how the law is applied to a specific set of facts.
A revenue procedure is an official statement of a procedure that affects the rights or duties of taxpayers or other members of the public under the Internal Revenue Code, related statutes, tax treaties and regulations and that should be a matter of public knowledge.