How about 1959? http://pitrading.com/free_market_data.htm This link has free daily data as a continuous contract from July 1959 to roughly present.
I have looked for data like this a lot, but haven't found any reliable source yet. Let me know if you find it, but I don't think you will. 59' is the best I have been able to do. Once you have the data the problem becomes verifying it, devising a way to check for misprints or errors and figure out how to roll it. 5yr
I am desperate. I search for the data from 1936 to 59 and can't find it nowhere. The only place i have found is payed and i don't know if it is ok to paste it here. It costs 100 usd and i am not even shure if i will get it if i pay (although it is through paypal) because it seems like this data don't even exists. In google images i have found only 2 images and the sites where they were don't have the data in numbers (http://crops.missouri.edu/audit/images/SoybeanPrices_MO_small.gif and http://www.choicesmagazine.org/magazine/fig/figure_86_full.jpg). I tried searching trough many ways and many places, and had no success. If somebody has this data please eather paste the link or contact me.