Legislative histories have been compiled by Hein Co. as well as by individual federal agencies and various House and Senate subcommittees. To locate them in the library catalog, search for "legislative history" and the name of your Act. A few examples are listed below.
The Congressional Research Service is a division of the Library of Congress that researches and produces reports on pending legislation for members of Congress. These reports typically analyze existing legislation on a particular topic along with its history. Previously the Library of Congress did not make CRS reports available directly to the public but a new law required that all reports issued in 2018 and beyond must be made available to the public. Older reports will likely be made available through the CRS website as well but for now various agencies and organizations do provide some on their websites. Other reports may be obtained by contacting members of Congress. See the links below for various collections of these reports.
Many government agencies and nonprofits compile legislative histories and make them available on their websites. Identify which agencies and nonprofits work in the area addressed by your Act and review their websites for links to legislation, publications or even "advocacy" pages. Keep in mind that nonprofits may have an agenda or point of view and that legislative histories compiled by any source (be it government or private) may not be 100% complete.
Law review articles often function as a compiled legislative history, listing at least the key pieces such as bill versions, hearings, committee reports etc. They may not be complete and are not likely to provide the full-text of the documents but they will offer citations to give you a starting point in building your own legislative history.
Practice guides and treatises sometimes include legislative histories either as part of their text or as a separate appendix. Simply find the leading resources on your subject and browse their tables of contents.