Umm, Pete is in Europe, no? Okay, an island off Europe, but so is Greece, and Venice.
If you're looking for wood JUST for a SB on a Standard, I'll go on a limb and say "Non-existent". You should be able to find a full set, but probably not a Koa SB. Keep this in mind so you can plan to buy the whole set in your search for a SB.
Now, if you happen upon a builder who has an unmatched SB that he (or she) is willing to part with (as Pete had already mentioned), then you're lucky, and should snatch it up.
Question: For a Standard, why would you look for a Koa SB and not a full set?