I am not in the UK, so some of the tricks might not apply to your case, but…
a) try buying a 160-200 g/m2 A4 paper (usually available in any colour: white, pastel, bright colours) or business cards paper. They usually come in packages of 100-250 sheets per pckg. Or buy a so called hammer paper (A0 paper) – in that case you would first have to have it sliced down to A4 sheets. Then ask somebody in photocopying shop or private printhouse to trim it down for you, to the 3″ x 5″ size cards. Or buy a trimmer. Anyway, it should cost you significantly less than buying originally cut index cards.

b) Perhaps this would be more applicable: try to find a shop where art & design students buy their papers, or some ‘hobby-shop’.

c) in some cases, private or other printint houses might be willing to supply you with their residue paper, e.g. leftovers for brochure soft-cover, etc. The thickness is the same as index cards, and you might even get a bargain

First, the ‘blank’ paper that I currently use has small dots very faintly printed in a grid every 5mm. It means that I can use the paper as graph paper, lined paper (in a horizontal or vertical alignment), Sudoku/Boxes/Logic Puzzles/Crosswords etc puzzle paper or blank paper, all on the same sheet. It’s so useful, and yet so hard to find- If there is a way to print this, I’d be hooked for life!

The only other thing is – A6? I know it’s a lot to ask, but I’ve tried reformatting the North American standard sizes and I can’t find a way to make any of them look good on A6 paper (or more usually, A4 quartered to A6). I’m so used to having an A6 notebook in my pocket; the index cards would be a good option if you can bulk-purchase paper in 3″ by 5″ format, but I’ve not seen this anywhere here in the UK. Anyone with advice, let me know!

Does anyone have suggestions for where on earth to find a 7-hole punch? I’m going to end up hitting the FranklinCovey store, I guess…