I doubt it's easy to get a hold of, but if you're willing to go the route of psychedelics, Ibogaine would be worth researching. It can be dangerous, so it's not a thing to take lightly or on your own, but it has (as far as my research has turned up at least) an unparalleled success rate when it comes to successfully kicking addiction and preventing/eliminating withdrawal symptoms.
Here is a pretty great documentary about it (Potential trigger warning as there is lots of footage of shooting up given that it is an autobiographical doc by an addict who is actively trying to kick). It's worth watching the whole thing if you can.