I know it's no consolation to losing something you have all kinds of attachments to but if you don't find the other earing, consider having the remaining one made into a pendant or have the stone reset into a ring. It's not the same but at least you still have one of the opals.

A word of caution though, opals don't like hot, soapy water. They will crack. Once cracked, the stones are pretty much toast. I know this as I cracked both of my rainbow opal earings when I took a blistering hot shower one day.