Below are some websites you may find useful. If we have missed any, please get in touch.
Go Stargazing
Use Go Stargazing to promote your outreach events and increase public awareness.
Search for events and Astronomical Societies near you.
Thank to Neill from Go Stargazing for providing the feed to the website.
Astro Speakers
Astro Speakers has a great list of astronomy speakers from across the country.
Speakernet
Speakernet is has a wide range of topics including Astronomy. It will require a search.
Dark Skies Matter
Dark Skies Matter seeks to reduce the prevalence and harmful effects of unnecessary, artificial light and to protect fragile oases of natural darkness wherever they are still to be found.