Administrative agencies have quasi-judicial and enforcement functions, and conduct hearings and issues decisions through administrative law judges.  The procedures and publication of these proceedings varies by agency. 

Official publications from the agencies resemble standard case reporters.  Table T1.2 in The Bluebook: A Uniform System of Citation (Reserve KF245 .B58) lists the official and commercial publications covering administrative adjudications, interpretations, and opinions of the major federal regulatory agencies. 

Agency websites may also contain the full text of its decisions.  A portal of "Administrative Decisions and Other Actions - by Agency" is maintained by the University of Virginia.

HeinOnline: U.S. Federal Agency Documents, Decisions and Appeals Library - contains many official sources for administrative decisions

LLMC Digital: This electronic database includes historical federal administrative materials, including agency decisions.

Westlaw: Federal Administrative Decisions All database and several CCH and other agency reporters found under Federal Administrative Decisons link

LexisNexis: Federal Agency Decisions, Combined database under the "Find Statutes, Regulations, Administative Materials & Court Rules" link

BNA's Law School Premier: database of agency information by subject area - includes some agency decisions and valuable current information

United States Attorneys General are the legal advisors to the executive branch and render formal advice in the form of opinions.  These opinions may be persuasive authority, but are not binding.

Opinions of the Attorneys General of the United States: (1791-1982) - HeinOnline U.S. Attorney General Opinions Library

Opinions of the Office of General Counsel of the U.S. Dept. of Justice: (1977-1996) - HeinOnline Office of Legal Counsel of the U.S. D.O.J. Opinions Library and (1992-present) - DOJ

LexisNexis: (1791-present) US Attorney General Opinions database

Westlaw: (1791-present) Attorney General Opinions database