A good resource for you to look at is the Plum Book. Every four years, just after the Presidential election, the Plum Book, is published, by Congress. The Plum Book is used to identify presidential appointed positions within the federal government. I'll add that it lists every position that is appointed by the President. In 2016 there were 9000 positions to be appointed. In 2012 8000 in 2000 7000. I think we can assume at this point that every 4 years the list gets bigger and bigger. If you go to gpo.gov and do a cursory search for the Plum book it'll give you the latest version. However, online it only goes back as far as 1996.