Platts will sell them to you...if you can't find a free source on Google. Try www.eia.doe.gov, you might find something there. If not try the 'contact us' link and contact an oil expert--they should be able to help.
Try the CRB Commodity Yearbook. A local library may have a copy in reference. N.B., there weren't energy futures around 50 years ago but you can get spot charts.