Poster sized coloured card - where to buy?

[Al&Em]

Hi there

Does anyone know where I can buy a large piece of coloured card or paper (poster size)? I want to use it as a backing for pictures/paintings that my son creates and for photos to put up in his room. Or is there a nifty alternative that I haven't thought of?

Thanks

[scareyt]

Cowling and Wilcox near Camberwell Green do loads of giant card and other art stuff.

[sillywoman]

Mr Green in the village.