I would challenge your assertion that drug users don't call 911 when they or another drug user overdoses. They do. Not as much as they probably should, but they do call. Maybe the police have a slightly different mentality up north of the 49th, but when the police attend OD calls, they're not worried about arresting people. I would say the largest barriers to addicts seeking help from heath care providers is the attitudes of health care providers themselves. The number of times I've had addicts refuse transport because, "they're all assholes in the hospital, they treat me like shit because I'm an addict," is astounding.
Again, maybe this happens more North of the 49th than south, but street narcan kits are quite prevalent up here. It's a little kit with 0.8mg of Naloxone preloaded in a syringe. I'm sure with IN naloxone becoming more common, the street kits will transition to that form over time.
The major problem however is that so few overdoes involve a single toxidrome. Most ODs are polypharm and opiates are but one of the agents on board.
If you want to look at public health initiatives that really do make a difference, read up on Supervised Injection Facilities. There are a number in Europe along with one in Vancouver, Canada and one or two in Sydney, Australia.