The chemicals to make it aren't that expensive. Even if you stopped China , you probably wouldn't dent the fentanyl trade. It might drive prices up a little but since so little goes so far, that hardly matters at the wholesale level.
And, of course, there's this fallback.
Nitazenes were developed in the nineteen fifties and sixties and were meant to be a substitute for morphine. But they were so powerful that the FDA didn’t approve them. Now they’re a schedule one drug and illegal just like heroin and LSD. Nitazines are made in the lab and are inexpensive to produce. They block pain signals in the brain by binding to opioid receptors in the brain, spinal cord, and other sites in the body.
Depending on the chemical formulation, some nitazenes are 800 times more potent than morphine and 40 times more than even fentanyl! They come in liquids, pills, and powder form. And just as illegal street drugs can be laced with fentanyl, they can also contain nitazenes without the user knowing.