That eighth-inch steel ball is known to zing off into an alternate universe. However, most fair size towns have a place that services bearings and that little steel ball is simply a hardened ball for a bearing. You can probably get them locally for little or nothing. Last summer I lost one, and went to the bearing shop in our hometown. The lady at the desk wrapped a piece of tape around her finger, stuck it in a box of bearings, and brought out five of those little balls. The didn't even charge me because I've been a customer before and it wasn't worth writing an invoice.
Look around locally, I"m sure you've got a place that will sell you some.