This page will offer little bit to your question.
ads-b-flight-tracking-f21/how-common-is-adsb-on-us-air-carriers-t17874.html
You can check some files for 2014 in this folder.
[The Y in the far right spreadsheet column = Aircraft equipped and sending ADS-B data]
Dropbox folder dropbox.com/sh/e2n3j7zl7s8a … h_ML8Nf0Ia