You can buy this package in both our digital store and Unity Asset Store. Please see the Buy Page for more. Although you can get full support from either store, we suggest you purchase it from our digital store to get faster update versions and support us a bit more :) Thank you.
You get all point release updates up to (but not including) the next major version. If there is quite great change in either Unity or the system webview, we have to rewrite almost all code and we will release a new major version for it.