talkmagic.co.uk

Someone PM'd me about this very question recently, I see that there are three main places which spring up on Google -
£4.49 · eBay
£7.99 · John Lewis
£6.06 · Zatu.co.uk

By a strange coincidence I was in our local John Lewis a few days ago and saw they were selling twin packs, one blue and one red, but there was no price on them - also no store assistant in sight to ask! At £7.99 they are rather expensive but the E bay store (JP Online) offered free P&P but still not exactly a bargain, I suppose if you just need a couple of decks then it's not too bad.

For a larger quantity, Costco sell to non-members, but you need to buy a couple of bricks.
19.99 per brick (delivered), minimum order is 2 bricks, and 5% surcharge for non-members, so £42 for 24 decks = 1.75 per deck.