Beta values for more than 1,500 companies are available in the Value Line Investment Survey. The latest issues are at the Reference Desk; the publication is on microfilm cartridges from 1969-1979, and on microfiche from 1980 onwards.
The Standard & Poor's Stock Reports (in Business Reference) and its companion, the Stock Market Encyclopedia, (REF HG 4921 .S68) only began including betas with the Fall 1986 issue. (See excerpt of this book).
The Ratio Comparison section on Multex Investor provides current beta data (among many other things) for most public companies. Start with a search for Quotes by stock ticker symbol, then select "Ratio Comparison" from the second picklist. Note that registration is required on this section of the site.