My company is interesting in hosting a company-wide volunteer day for
150-200 employees.  I was wondering if you have any activities available for
this size group, such as park clean up.  Could you please provide any
information you have available about volunteer opportunities?

If you contact the San Francisco Parks Trust, which is located at McLaren Lodge in Golden Gate Park, they can assist you in volunteering at the park. They organize and help others organize clean up days, gardening projects, and other volunteer opportunities. Their contact information is 501 Stanyan St; (415) 750-5105.