All the Artist Proofs and Pre-production samples are very tightly controlled. They are available to the artists for review and are controlled by Stephen, who is in charge of all WDW Pin activity.
They may be made available for pin events, pin auctions, special promotions, or giveaways at something like Scoop's Pin Talks. You would not find one for sale at any pin location. If they end up being traded away either directly or onto a CM lanyard you are bucking million to one odds.