On the T-Mobile forum the staff note:
The HD2 has been very popular and is currently sold out in many locations. We are working as quickly as we can to secure additional inventory. We will post updates here on when additional inventory will be available.
Some Retail stores may still have inventory. If you live near a T-Mobile location, you can contact them to see if they have inventory remaining.Click here for a list of T-Mobile locations. We suggest you contact stores via phone before visiting to see if they have inventory on hand. If they do not have inventory, they should be able to take your name and notify you when they have stock in stores.
Good luck to punters trying to find this very desirable device. Looks like T-Mobile has a hit on their hands after all.
Keep an eye on the T-Mobile blog for availability updates here.