Where Can I Buy Boxes to Ship LP's In?

I have some LP's I would like to sell, but I need boxes to ship them in. Can anyone tell me where I can get the type of boxes that Music Direct and other online retailers use?
$1.68 per mailer... and some folks ask why LP's are so expensive on the 'net when you can buy'em cheap locally? The mailer plus your time and it doesn't make sense to sell'em for less than $5 a copy. There ya have it folks!