Not strictly a Sunbeam event but the mark is usually well represented. Usually 100 or so Vintage bikes held at Beaulieu Motor museum. See Sunbeam MCC website for details
http://sunbeam-mcc.co.uk/
Some pictures from past events.
(http://imageshack.us/photo/my-images/21/wckr.jpg/)
(http://imageshack.us/photo/my-images/809/qjqc.jpg/)
(http://imageshack.us/photo/my-images/833/md4s.jpg/)
(http://imageshack.us/photo/my-images/826/vxt3.jpg/)