I can obtain as many as I like from work. Don't bother for commuting as its 10 minutes max, so only use for going for a spin. The thought of re-inserting them with ear wax/grubby fingers etc. is a bit gross! The only time I would re-use is at a fuel stop where I take my lid off. Other than that, chuck 'em! They come in sterile packages in pairs: http://www.screwfix.com/p/peltor-nex...00-pairs/28317
Tip: keep some spares in your jacket pocket.