Where can i download jam pack 4 (orchestral sounds) for garageband 6.0.5. please. I have an air book maverick OSX 10.9.4. Thanks

This JamPack is no longer sold separately by Apple. You could search for the boxed retail version of the JamPack at eBay or Amazon.

But it is much more economic to install MainStage 3 instead. You can buy it at the Mac App Store. MainStage 3 will install all five JamPacks for a price much less than the price of a single JamPack used to be. Afterwards the JamPacks will work with Logic and GarageBAnd as well.

Just launch MainStage after installing and use the command "MainStage > Download additional content" and select the JamPacks you want to install.