On the website of VSL you can buy the standard library or the full library (that's the standard plus extended library). When you buy it there, you have to login and when you have registered the standard library, the full library is priced as the extended library. There it is not possible to buy the extended library without having the standard library. (Of course you can buy the full library at once).
I don't know if it is possible elsewhere just to buy and install the extended library (that is the upgrade from standard to full) without having the standard library.
Hopefully somebody of VSL can answer that question...