The CPI is based on surveys conducted by BLS (Bureau of Labor Statistics). Those surveys collect price information which is reviewed by commodity experts. Those experts review (and possible adjust) the data based on their knowledge of the particular commodity. That adjusted data is then averaged to calculate the CPI. You can definitely get the values that ...
Index Mundi has a lot of commodity data (present and historical) available to the public.
But I am not sure if you would find toilet paper on the list (lol) - it does not exactly fit the definition for a commodity:
"a raw material or primary agricultural product that can be bought and sold, such as copper or coffee."
Everything dvogel wrote is correct. Note that on the ftp page there are several datasets (including "ap" and "cu") which are labelled "consumer price index."
The Bureau of Labor Statistics (BLS) samples posted prices at various US businesses on a monthly basis. This sampling includes roughly 85 thousand observations per month. The BLS then creates and ...