Active at 1 microgram. Daaaaaamn! I'm pretty certain most vendors want to stay in buisness and not kill off their buyers.
Even if you're in China, you're not going to risk making this. First of all, you'll need special equipment so you don't kill YOURSELF in the process. Then special procedures for shipping so the couriers don't drop dead. Then you have to worry about the blowback from governments hunting your ass when their citizens start dying in droves from the product's inevitable distribution as street heroin. Remember all the fake junk spiked with just REGULAR fentanyl a few years ago that killed masses in the US? Remember how that ended? yeah... Expect the same if you're in China, India or wherever. You'll need a black market chemist if you want this stuff. Best bet: become one.