In the majority of US states you can order interleukin 6 testing online and have the blood drawn at a local blood draw center (see my general overview of the process).
I'd suggest ordering from Life Extension because they have the cheapest price I know of ($75), and I've been happy with their service. You can also compare the other 2 interleukin 6 test providers I've found.
Take a look at my state-specific issues page if you're in AZ, MD, NJ, NY or RI.
A few of my notes on IL6: