If you are looking for a science presenter to take part in your event you can search this directory of presenters by location and subject area. You can also register yourself as a presenter.
The British Science Association
The British Science Association is a charity which exists to advance the public understanding, accessibility and accountability of the sciences and engineering. They also coordinate National Science and Engineering Week each March and produce Challenge Packs full of activity ideas.
STEMNET operates regionally and acts as a broker between schools and STEM engagement activities. STEMNET also runs the national STEM Ambassador scheme which provides training, help and support for scientists and engineers who want to get involved in outreach activities.
British Interactive Group (BIG)
BIG offers loads of resources related to interactive hands-on science. You will be able to find show scripts and advice on presenting to audiences, along with information about interactive exhibits and where to find your nearest science centre.
Psci-com is a very active discussion list where people involved in all kinds of science communication and public engagement with science share information, ask questions and discuss topics.