How do I export each track as single BWF file?

Nothing in the manual.

When I export a session I can only export wav, aiff, caf, w64, and raw.

How do I get the bwf option?

Thanks Philip

Its a good point. Its not handled in any release version at present. Sorry.
Ardour will save its own recorded audio in BWF format (see the Options menu), but this is totally different from export. However, it does mean that you can bounce each track (1 by 1, unfortunately) and the newly recorded track will be in BWF format (if you requested that as the “native file format”).

Please file a request in mantis that this be added to the export system.