Hard to pre order a case when it seemed as though most manufacturers weren't aware of the slight design change. If you're preordering then you're lining up for a product that doesn't even exist, which would be tough. You could be waiting longer than you would if you just bought a case today.
There are many options out there today. May not be as many as there were for the other iPads but you're just over a week past launch so what can anyone really expect?