The problem with using Reddit specifically is that you can't filter by date anymore. Reddit has poisoned their results to show old posts with new dates on Google.
Huh, I wonder, can I download reddit? Like, all the text posts, ignoring images. I wonder how big of a db that is and how hard would it be to crawl it myself. It can't be more than a few gb of data. I mean, at this point there is a lot of information there that is just begging to be leveraged.