I'm not sure where you'd get them from, shivvy. You'd need to look around. I only know I've got a couple that are about an inch or so thick, but I've had them for a few years and I can't remember where I got them from.
I have found these:
http://www.glsed.co.u...6+FILES&catRef=314554 . You may want to search for something similar, although this one isn't cheap. I have seen others around at less than that, just can't remember where. I think they're fairly common, though.
I don't think you can get A4 sized plastic wallets that integrate the hole strip into the A4 dimensions. That would somewhat defeat the object, because you can't readily get the paper that would fit them, unless you used foolscap, which is narrower, but also longer.
I'm still wondering whether a display book/presentation binder wouldn't be your best option.