UK shops (quick google):
http://www.disc-shop.co.uk/
http://shop.cd-writer.com/acatalog/ALL_PRODUCTS_L...IBE_MEDIA_929.html (<= 50pack available)
In Belgium, most stores I know have them. Though, the maximum I've seen are 10packs. Then again, spindles of more discs wouldn't be bought so much anyways, so why would a store buy them in and sell them? (though, in the future, I'm sure they will be widely available. IF lightscribe gets popular, because that still remains to be seen). Dunno how this is for the UK, but I'd imagine it would be roughly the same.
Best bet to get your hands on big spindles are webshops I guess.
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