You could try Silverprint in London (
www.silverprint.co.uk). The range is not as extensive as Light Impressions and they are more expensive. You could also try
www.plasticsandwich.co.uk for something more exclusive (and more expensive again). Silverprint do exactly the same kind of clamshell boxes that Alain Briot refers to and does the polyester print sleeves. You could also take a look at Secol (Royal Warranted) who manufacture print sleeves and have a range of portfolio items (
www.secol.co.uk).