Maybe you know someone who's been to rehab? I believe it's also available on the dark net. If you have a friend from the USA willing to mail it to you they cab pick it up at any pharmacy.
You could probably go to an urgent care ask a random doctor.... Not er (A&E?), but someone you did see instead of your primary care or during transition periods. Maybe even just say you have a friend who refuses to be safe while using and they won't admit it when you hang out, but they are always nodding out and you want narcan on hand in case one day it's not enough even if after his lips turn blue your rescue breathing* and calling the ambulance they still can not be revived while they might have if you had narcan on hand. Due to confidentiality issues I'm sure your doctor deals with just like doctors due here they can't share the issue unless they are in immediate danger, which would be such a stretch without names they will likely not do anything.
I can't say for sure so don't take my advice as guaranteed you will not run into any legal issues as definitely it will likely be considered an issue if found in your mail. Nor if any of my advice on prescribing information is correct. I think this is really as much information here with sourcing and prescribing advice rules here that exist, but I think you can figure something out.
*rescue breathing: unless they have a infectious disease or virus take a paper towel with a hole poked to prevent contact, but allow you to inhale air then close their nose and exhale into them, repeat as long as possible until doctor comes and declares as they just aren't breathing, but if it's done for them brain activity can continue if the body gets enough oxygen exchange in the manner like for without the chest compression as that would force out air)