The President may generate a variety of materials related to legislative bills, especially signing and veto statements.
Presidential materials are compiled in a variety of sources, including:
HeinOnline has extensive PDFs of presidential materials:
ProQuest Congressional also provides PDFs of many presidential materials:
You can also access a large collection of presidential papers for free online:
Both Lexis and Westlaw provide access to presidential documents. If you have a citation to a specific document, it's generally better to access it on HeinOnline, which is more comprehensive and provide PDFs. However, if you'd like to search for presidential documents by keyword, Lexis and Westlaw do allow you to perform more sophisticated keyword and terms and connectors searching.
Finally, the UCLA Law Library also owns print copies of presidential documents: