In this system, you have drops. How does a rival gang know where they are? They'd have to buy the product to discover the drop and drops shouldn't be used multiple times. They could watch a user find one, but then that drop wouldn't be used again so they couldn't stake out and wait for their rival to refill it.
I think it's very unlikely a drug business can get to scale without reusing drops; the cost of scouting a good drop is significant, and the number is finite. Regardless, the value of a drop declines the farther it is from customers and from the dealers who supply the drop. So in practice, gangs will still have an incentive to claim turf and to harm other dealers using drops on their turf.
Even if that somehow doesn't happen, they'll still have the same strong competitive incentives. So they'll be very much inclined, as now, to discover rivals and take over their business through violence.