Where can I find...

Try Gumtree

or ask at any big shops

You need them to be strong, so the sort of thing you might ask for from the local shops will be for crisps etc.

I got a load of strong ones on the internet (they actually do two different strengths).

Best thing is to go to the post office, where they do lots of sizes, which are decent value.

Ok thanks a lot!

Those storage companies sell boxes at reasonable prices.

Outside the back doors of most large Supermarkets you will find them stacked in big wire-sided trolley thingys, waiting to be taken away to be recycled; ask nicely and they`ll happily give you as many as you like. Saves staff a bit of work and you get to `recycle` them, everybody`s happy.