A guy i used to train with years ago used to work for the IOC (international olympic committee) and he said it was commonly discussed that many trainers had access to drugs that would not show up in a drug screen. Remember that in order to test for a certain drug, they need to know what to look for; it's not like they can just test for everything on the planet all at once. There are thousands of PED compounds that would never show up a drug test for PED's. The problem is, once someone gets wind of the compound being used, it gets reported to the IOC and they add it to the drug screen.
I know for a fact when i competed in power lifting years ago, that guys were admitting to using compounds that could not be seen on a normal drug screen for PED's. As these new compounds are leaked to the public, they will also be added to the drug screen.
And yes, S&C coaches are well known all over the world as being drug dealers or someone to point you in the right direction. When i was in high school i played football for a power house school that was known for being one of the top 5 football schools in Texas. There were plenty of kids jacked up on Test and Deca, some of the coaches knew about it, but i don't know if they had anything to do with it.