In the majority of US states you can order reverse T3 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 ($55), and I've been happy with their service. You can also compare the other 5 reverse T3 test providers I've found.
Take a look at my state-specific issues page if you're in AZ, MD, NJ, NY or RI.
The American Association for Clinical Chemistry has basic summary of reverse T3.
A site called Stop The Thyroid Madness has some opinions on levels and ratios and suggestions for influencing them.