Paperclips

How many paperclips are in circulation at any one time? I think I have bought a packet of paperclips perhaps once in my entire school and working life but always manage to have an overflowing collection of them in an assortment of useful sizes. At a meeting today someone collected a single clip off the desk at the end and said I'll have that it's a resource. Which it is. But who supplies them all if we don't actually buy them?