The Library of Congress has 84 of these programs in our Recorded Sound Collection. They date from 1948 to 1951. You can search the online database at http://star1.loc.gov/cgi-bin/starfinder/0?path=sonic.txt&id=webber&pass=webb1&OK=OK
The programs are simply called "Boston Symphony Orchestra Rehearsal."
The programs are available for public audition, but only in person. From your e-mail address, it looks like your in Utah, which means a long trip for you! If you're planning to attend the ARSC Conference in May in Washington, you could make an appointment to hear them in the Recorded Sound Reference Center at the Library.
Feel free to contact me offlist for more information. A reference librarian may able to help you research these programs further.
Library of Congress