I have been trying to get one for days - and finally saw a store about 30 miles from my house got one in stock so I bought it online with in store pickup. I can't get there until Tuesday but bought it sight unseen since nobody has had them. I would suggest you keep checking in store availability of the stores near you - especially since they are so hard to get.
The store availability tool online seems to be a bit off.
According to the tool, none of the silicone cases are in stock and won't be until for a couple weeks. I took a trip to the Apple Store (Portland, OR) and they had all cases in stock. A couple had 2-3 left, while certain colors had more than 10+.
I would try calling the Apple Store for a confirmation on the stock levels.