This is such a good question. I think, like many things, the time to find that group is *now,* not after the SHTF later on when everything’s chaos. I do know from all my reading that the ideal number for survival is NEVER just “one.” There is too much for one person to do (even just guard duty, you can’t watch 24/7 or you will burn yourself out quickly), so finding a group is quite important.
I have few family, and none close to me geographically. If SHTF hit the fan tomorrow, I like to think that my area (Portland, Ore., USA) is hippie enough that many people here are already preppers to some degree, just by the way they currently live. There’s definitely a sustainability vibe here, and that is a good start.
In fact, I think finding others right now might be best via simple observation. The woman down the street who’s about my age who also vegetable gardens and hangs out her laundry to dry in the sun is a definite possibility, because she’s already living to some degree with fewer socially-based resources than many suburbanites (such as grocery stores and electricity). Likewise, anyone whose back yard appears to be junky but at least somewhat organized is probably someone who finds alternative uses for items rather than discarding them and contributing to waste, so they might be a good bet, too. They have a mind geared to look at alternative uses and possibilities, and skills like that are very useful.
So that might be a place to key off of in the search. I don’t think I’d tell these people I’m a prepper, but maybe take the opportunity to get to know them (bonus: they are outside a lot, doing things like cutting down trees or tending their gardens or hanging the wash), so that if and when the time comes, while they may not be prepared in the same ways that I am, they will at least be more resourceful than most people, and likely have some ingenuity to bring to the table (mechanically-minded people, for instance, who are the very ones that currently annoy me by making loud noises while working out in their shop all day long ).