Don’t forget that you’re already collecting registration and last used IPs, so you can already infer geography to a degree from that kind of data.
You can also create opt-in groups for each geographic region. If your users benefit from you knowing their whereabouts then it shouldn’t be a hard sell.
Finally you can provide direct generic links to the user profile for them to visit directly. Discourse has a special /my/ path which will take users to their specific page.