But it probably could be, if there's a market for it. There are trained chemists making meth [0]. The sale of the precursors of fentanyl is controlled, but so are the precursors to meth. If fentanyl (or an analog) stays popular we'll have people making their own.
Edit: I'm not saying it would be as obtaining PSE, but if you're a member of a chem lab, the only thing between you and an order to Sigma is ~two signatures? There's too much money involved for it to not happen.
[0] http://news.sky.com/story/inside-the-cartels-cooking-crack-i... (I know, Sky News..)