According to this article there are 30[1]. Another whistleblower allegedly committed suicide two months ago [2].

[1] "Aside from Mr Barnett and Mr Dean, there are some 30 Boeing whistleblowers, including Mr Salehpour." https://theloadstar.com/im-scared-says-boeing-whistleblower-....

[2] https://en.wikipedia.org/wiki/John_Barnett_(whistleblower)