Regulations.gov (2003 to date):
Search by the federal agency's docket ID number (e.g., CMS-2012-0152) found in the preamble to proposed and final federal regulations to locate comments submitted on a particular regulation.
Agency Docket Centers: Older materials used in a rulemaking or other agency action may be unavailable on Regulations.gov. Search government agency websites for docket centers or repositories of documents related to a particular rulemaking. (For example, the U.S. Environmental Protection Agency (EPA) maintains a docket center.