There is no need to download any Hebrew fonts, OS X comes with lots of them already. All the letters are there, you just haven't found the right keys. Tell me which letters you are missing and I will tell you how to type them.
But Pages is not a good app to use for Hebrew, it has bugs that make it unsuitable for RTL scripts. Better to use Mellel (the best) or TextEdit, Nisus Writer, or Open Office.