A few years ago when rumors were flying that the fda was going to crack down on a lot of that stuff I bought a large amount of piracetam for a cheap price. They were getting rid of it. I still have most of it left. Best bet is to find a place, perhaps overseas, that sells it and is willing to label it as something else. That should get past customs but you never know. The worst thing customs does is confiscate the item, they never go after the person who ordered it because its so hard to prove. Now if it was heroin and you kept ordering, that might not hold true.
From what I understand, customs is way overloaded at any given time. When a suspicious powder is seen, unless they have a tip or something they will just use a quick narcotics test that looks for common opiods and stimulants. If its not a hard drug they have little motive to find out exactly what it is. If it says powdered vit C or some other common compound, they are not going to send it to the lab to see if its the right thing. I did have a supplier in china one time who told customs what it was, told them on the phone even though it was labeled something else. Nothing happened to me
The trouble with china is they cheat all the time. If they can save a buck they will and quality is not assured. If something is not expensive per gram, they have less incentive to dilute it or substitute something else. Something that is $20 per gram, watch out