Betterment and Praxis

Unfortunately, you basically listed the 2 most effective ways to do this as unavailable: local community and family/ friends.

Has anyone here read about, or practiced, any methods for deescalating, defending against, or getting out of such situations without having to ask the police?

Yes, very much so, but it's not simple stuff you can impart in a forum thread. I've gone through several de-escalation courses while working for a university. Actual de-escalation training is (or at least, should be when done right) very technical, because there is a lot of variability in your methods depending on the situation:

• Does the person appear mentally sound? Mentally ill? Under the influence of a substance?
• Are they responsive to you when you speak to them?
• Are they scared? Angry? Belligerent? Violent? Distraught?
• Are they injured and in need of medical attention? Is anyone else?
• Are they armed? Is anyone else? Are you? (Last one is very important, because you need to avoid getting into a physical confrontation if you are armed, both for their and your safety.)
• Are you trying to direct their attention away from something/ someone else?
• Are you or someone else the direct subject of their attention?
• Are they indicating an intent to self-harm?
• Are you or someone else cornered?
• Are there other people around who can help?

Any of those things (and more that I'm not thinking of off the top of my head) can change how you approach the situation, and the actual methods of de-escalation are very complex on their own.

You can take courses in de-escalation on your own, if your job is presumably not providing it (avoid de-escalation courses paired with, rolled-into, or run by self-defense trainers, imo. Look for ones that specialize in preparing teachers, medical staff, and care and social workers).

If you don't have family or friends around, I highly suggest introducing yourself to some neighbors. People are often shocked how much neighbors want to interact as a community, but most of the time no one ends up taking that first step. Plan a meet-and-greet for your apartment complex, go around and introduce yourself door-to-door , with some cookies, etc.

DO NOT lead with "I'm looking to find a group of people to be a local community intervention and defense group, to avoid having to bring police into situations we can handle ourselves." You'll get the wrong people interested. xD

Lastly, self-defense is important, and you should know how to defend yourself and others. Don't fall for people telling you martial arts are useful for this. BJJ is useful if someone else grapples you, but you want to avoid getting into that situation as much as humanly possible.

Retreat is always safest/best. Ranged defense is second-safest. Hand-to-hand is not at all safe. Take that as you will.