Get a node and see who's in your area. They're pretty cheap and there are good prebuilt ones if you don't want to DIY. Make sure to get the right frequency for your region. In USA we're on 915 MHz.

UK apparently has a large mesh. It got so large they were having congestion issues. I should note that, though I can see all these nodes I often can't get messages out to the mesh. I'll be installing a yagi soon since I have a nice but narrow view of the valley.