The people who advertise on Ebay under the name exotichawaiianwoodworks
would be able to help you. They are good to deal with, based on my experiences with them.
There is a member: bib808 who has sold koa & other Hawiian wood in the past. He was last active on IAP 6 months ago, so you might try an email thru the public profile > contact approach.
Every blank was very high quality! I believe I bought 10, and it's about time for me to order more. Most went to friends in California that served in the Navy for a time in Hawaii, and fell in love with the wood.
A couple of weeks ago I picked up a great curly koa board, intending to make it into pen blanks. Haven't touched it yet. If you're still looking for these blanks PM me and I can cut you some.