Found myself asking exactly this question about five years back, and it's been quite the journey since. The truth is, most communities worth finding aren't advertised on billboards—they're discovered through doing.
Started by just attending renewable energy expos and tiny house festivals. Met some absolute characters at the Ecobuild events, and a few of those connections led to visiting actual setups. Nothing beats seeing someone's Victron system running in anger or watching how they've configured their water storage. You learn more in an afternoon than months of forum scrolling.
Then there's the local angle. Contacted my council's planning department, believe it or not—they knew who was pushing for change locally and could point me toward planning applications for alternative dwellings. Found a micro-community about 20 miles away this way, and we've since become proper mates.
Online communities help, obviously. Reddit's got some decent UK off-grid subreddits, and the Facebook groups can be surprisingly genuine if you're willing to wade through the noise. Just be honest about what you're after and whether you're genuinely exploring or just curious.
The other route: start something yourself. I run an informal monthly meetup in our region where people bring their problems and their wins. We've got a solar designer, a plumber who understands greywater, and someone who's basically keeping their Fogstar batteries alive through sheer stubbornness. Word spreads.
What's drawing you to this? Are you looking for actual neighbourhoods or just people who get why you're interested in this stuff?