This DVD set is currently available at the Disney Store online. However you must be a member of D23 to purchase this set. You can join when you place your order for the set. The Disney Store changes up links quite a bit, so I don't want to post a link directly to the item.
If you are at the front page of the Disney store search for 'D23 Walt Disney Treasures'. That should take you to the page where you can order this. It will let you know if you need to join D23 or not.
To join D23, it cost about $75.
This DVD set is about $500. Yes it is expensive, but if you do not own many of the individual treasures, it is far less than buying them off the collectors market.
If you decide to order, I would encourage waiting until free shipping or reduced shipping is offered. They charge a premium to ship this set.
Also, you get 2500 Disney Movie Reward points with this purchase.