Addendum: oh my ghods people want HOW MUCH for the dear things? Somebody's actually *parting one out* on eBay, separate listings for the upper shell, lower shell, button and ball ring. O.O
(No ball. I presume the trade in computer mouse balls is heavily restricted under local Digital Aphrodisiac laws...)
Sadly, I no longer have my old one, but that thing was a tank!
@Momentrabbit I wouldn't be surprised to find @Rabit has a drawerful of them..