We accomplish this by creating a central email@example.com account where we create a bunch of calendars in. One of these is /Company which is a company calendar. Then we share it to our entire domain read-only
At this point your users would be albe to find it in the share discovery within preferences, or you could use zmmailbox to mount it for every user.
zmmailbox -z -m firstname.lastname@example.org mfg /Company domain domain.com r
ufortunately there is no way to make it mounted for new users you create through the web interface. If you script user creation though you can do this.