You can also sometimes find contracts via Google searches like these:
Boeing "collective bargaining agreement" filetype:pdf
"International Brotherhood of Electrical Workers" "collective bargaining agreement"
grocery OR supermarket "collective bargaining agreement" filetype:pdf
Google Search Tips:
Use quotes for exact phrases.
Advanced Search will allow you to enter alternate terms (grocery OR supermarket)
Since agreements are often posted in PDF format, it can help to use an advanced search feature to limit results to PDF format.
These are usually long documents, so they can take awhile to download.
You may find sites that sell documents for a fee--but the same document may be on another site for free.