Two problems here. First, real-time futures price feeds are not free. At least, not free for re-publishing. Second, and more serious, commodity futures go by expiration month. For instance, CLX4 is WTI oil with November 2014 delivery, CLZ4 is WTI oil with December 2014 delivery, etc. They have different prices. Which one should we peg to? A natural choice would be the front month contract (i.e., with nearest expiration date). But then we have a price jump at every roll (when the front month expires).
Alternatively, we can agree to peg to some commodity ETF (USO for oil, for example) but they do not really trace oil futures price as they have slippage due to roll expenses and management fees.