Got back from Smyth's in Cardiff while ago with Scene It: Lights, Camera, Action for only £14.99. This is the full retail pack which includes the 4 big button controllers. I was also pleasantly surprised to find that there are 8xAA batteries in the box so you're ready to play out the box.
You can check Smyth's website to see if there is any stock in stores near you. I've just looked at a few locations and it looks like its in stock in a selection of stores.
And if you enjoy it then you can save money on the sequel, as you can buy the game only instead of game + 4 more controllers. Hooray!