If you are looking for a Windstone sculpture or color that is not available through Windstone Edition’s online store, the best place to look is on eBay. You can also look through the most recent sales threads here in the Flea Market (however, if you find something for sale in a thread that has gone more than 10 days since the last reply, you should PM the seller to ask if the item is still available–don’t reply to the thread).
Other resources:
Official Windstone Dealers
Craigslist
eBay Classifieds
eCRATER
Etsy
Forum members are also welcome to post their Windstone-finding tips here.