Actual Contico boxes with the black handles? No - apart from Cornish Crispa who just do the small ones.
Really Useful boxes are similar, with locking handles that clip over the lid. Staples and Rymans do them, and there's also someone on Ebay who does them in bulk.
If you mean standard plastic storage boxes - Wilkinsons, Warehouse Clearance shops, most large supermarkets and DIY places will have them - some are better than others though, and not many have securely locking lids.