Weather Underground is a great site, although finding the specific link for archived METAR reports is more difficult than it should be. The following link is an example that gives all METAR reports for a given airport on a given day; you can either use the fields given on the page to find other dates & other stations, or you could edit the URL itself to find what you want (and perhaps even automate that into a screen-scraping app):
Weather Underground Link
You can also get the same data in a CSV file with a separate link.
If you don't mind doing a little bit of coding, you can also subscribe to their API, which allows you to get historical data with some fairly straightforward calls to their API. The "developer" subscription is free but limited in how many calls you can make; more expensive subscriptions allow more calls. The following link is where you can start learning about their API.
((This answer is as much an answer to this question, which is now closed and marked as a duplicate of this one. It is a slightly different question, and this answer is really more aimed at that question, but it addresses this question as well.))