If you really want to do it and you really fee like exposing yourself to the general public with regard to your illegal activities, start making some phonecalls, there are plenty of labs out there... you might need a reference sample (one you KNOW is good)... it might be harder in the US than it is in Canada as possession of steroids is more of an offence in-and-of itself... but it's a fuckload of trouble, time and effort. Probably better off finding stuff that works and sticking with it.
You run into guys all the time that _claim_ they get stuff tested or that their friend/dealer had it tested but it's probably bullshit.
Guys that DO actually get stuff tested are probably going to keep it to themselves as to who does it and what it costs.
Sorry if this isn't the post you were asking for but it's the way I see it.