Try Analytical Research Labs (ARL). They generally require that a medical professional order the test. But if you ask nicely they may allow you order one on your own.
Possibly the best use of a hair test is as a screen for heavy metals. The use of hair testing as a screen for long term exposure to heavy metals appears to be gaining wider acceptance in the medical community.
An ARL hair test picked up a near toxic amount of copper in my system. It turned out that my well water was naturally acidic and dissolving the copper pipes in my house. So, yes, I believe that a hair test can be helpuful.
I had a water neutralizer unit installed in my water system.