Does anyone know where I can find old TFRs?
As you know, a TFR is published in FDC NOTAMs, so you can use the FAA's NOTAM search tool's "Archive" mode to search for past TFRs issued via FDC NOTAMs. 

Use this link (https://notams.aim.faa.gov/notamSearch/nsapp.html#/). Press the Location button on the left and select "Archive Search." Then select a Date and Location designator to search for the NOTAMs (including TFRs) in effect on that date in that area. 

By way of example, I did a search for Riverside Municipal Airport (KRAL) on 2/2/2016, and it returned these old NOTAMS (included TFRs).  See the California Speedway TFR.