That’s one way to do it. The other is to leverage your network (if available to you) and ask people if they can refer you internally. I’ve had a lot more success with the second method.

How common is such a test in the US? I work in the US and so far, I’ve never been asked to perform a drug test, ever. Then again, maybe I’ve been lucky…

but is it really unlimited? At my last job, it was “unlimited with manager’s approval”, which basically means as long as the manager approves you’re good to go, no hard limits, but in practice managers wouldn’t approve more than 2-4 weeks (10-20 work days) a year, usually.