Where can I download pages templates - esp. fax templates?

Check iWork Community for user-contributed templates. You could also use any templates made for Microsoft Word.

Fax Templates are relatively simple.

Just find a suitable Word fax template and open it in Pages, amend it and save it as a Pages template.

Peter

If you want something much more aesthetic, and are willing to pay, look in the Mac App Store which has cheap sets from Jumsoft amongst others.

Peter