The Internal Bluetooth module is available as an upgrade kit for PowerMac G5 (Early 2005). You can see if this is your model of Mac by checking the EMC number on the bottom of the computer, it should be 2061 for these PowerMacs.
The module should also work in other PowerMac G5s (I've seen one put in a Rev A PowerMac G5), but it is in no way supported by Apple like that.
The part number is M9984G/A, however it is only available to Apple Authorised Service Providers.
- proton