The ‘search’ box hidden at the top of the screen does search through users, Ally, though I haven’t worked out quite what order they come back in.
You might find it easiest just to email the group page URL to your Cambridgeshire contacts, to be honest.
Those page references numbers seems to stay pretty fixed. [Though they need to log in at the front page first.]
This might also encourage people who haven’t signed up to register.