I'd say Strike Map would be a good point of call - are you in their regional Strike Club WhatsApp group?
They've also got a form here where you can sign up to their reps network:
Sign up using our form to join our network as bring together all those leading struggle into a reps/stewards/strike leaders national network. This network will share tactics, strategies and resources.
actionnetwork.org
I filled it in, found out it was Slack-based and then couldn't be arsed to go any further, but that sounds like what you're looking for?
Also, perhaps an obvious one, but try checking your local trades council - some of them are pretty moribund, some are a bit less so, but if there are people interested in similar stuff in your area then you might well find them there?
Oh, and to plug Ian Allinson's book tour as well:
workers-can-win.info
Dunno what your plans are like for tomorrow afternoon, but sounds like the London launch of his book is tomorrow, co-hosted by two Unite branches, and that might well be a very good place to meet other union reps?