If an employer does not provide a bulletin board at the workplace, do the employees have a right to provide and mount their own bulletin boards?

Employers are required to post certain information.  They do not have to
allow workers to post their own bulletin boards.

First of all,
the federal government of the United States requires employers to post certain information for
employees to see, though not necessarily on a bulletin board per se.

[F]ederal employment laws require employers to post notices ... that
are conspicuous and accessible to all employees. (shrm.org)

This information includes laws, and especially health and safety information.  For
example, all...

href="https://www.osha.gov/workers.html">https://www.osha.gov/workers.html
href="https://www.shrm.org/pages/custom404.aspx">https://www.shrm.org/pages/custom404.aspx