Pinball Center do some nice neons.
http://www.pinball.center/en/shop/pinball-parts-by-game/cirqus-voltaire/?sSort=1&p=2
They do certain colours so it may be a good idea to use this as a guide. As I recall with the purple one I ordered it seemed very slightly short!
YEARS ago I got hold of a multi coloured neon that had 3 or 4 colours that merged real nicely together. I do not have a photo sadly.
Be excellent to have a UK supplier - maybe you should contact Phil at Pinball Heaven as he is the UKs largest supplier of parts. He may distribute them for you.... You would have to have a chat.