Best place i found for TDK's is here:
www.kvjfairdeal.com
They are a shop in East End of london, they have a website that is more expensive than shop.
Shop is chq or cash only, mailorder carriage up to about 500 discs is £5!
Ask for Anej (ARNEJ is how it's pronounced), best to buy at least a box (to get best price) which is around 120 discs, shou cost you less than £50 delivered!