Social Shares (sort – postmeta)

These Sharing counts are not stored on post meta; they’re queried directly from Social Networks on each page loaded and added to the buttons via Javascript:
https://github.com/Automattic/jetpack/blob/master/modules/sharedaddy/sharing.js

You could, however, create your own little plugin that would follow the same method to query the sharing counts, and then store them in a custom field to be able to use them later.

I hope this helps.