Found it! I picked it up from P&C some time ago with one of their accessory-bundle sales. "pick a pouch, 2x tins, a lighter..." kind of thing for one price that beats their individual costs. You can find it as the 2nd pouch listed on this linked page, called 'compact box pouch'
it folds flat when empty, but here's a picture of it opened up for filling (or emptying) It certainly keeps the tobacco fresh a long time.