polygon.io: only goes back 5 years (according to their pricing page). tickdatamarket.com: I couldn't find SPY in their list of data. tickdata.com: option data only back to 2020-11-16, though that's quote data and maybe they have trade data back farther. I stumbled across thetadata.net. They appear to be fairly new, but it appears they have what I need back to 2012-06-1 and up to 15 minute delayed present. I'm giving them a try.