I've used data from Brian Burke's site before. I think it's the exact PBP data the NFL has, but you'll find that the structure and common phrasings change over the years. I had to write a lot of regular expressions and I was still catching edge cases for weeks.

btw, pro-football-reference has pbp data now too, and it probably goes back a lot further, but I think they discourage mass scraping of their site.