For drugs like MDMA from cooperative chemists
For drugs like cannabis from neighbourhood indoor growers.
For drugs like synthetic opioids (ad Ketamine) directly from the pharmaceutical companies.
For drugs like cocaine and natural opiates they are imported from revolutionary groups mostly. This one is tricky, as the other end of the trade tends to be fairly brutish, so there is a thriving "middle man" business.
I do not get your point.
My point is that dealing illegal drugs is a community service. The laws are complete bullshit, no body with half a ounce of sense thinks they are socially useful, they are maintained for reasons of brute power and political lag. They are failing