Mackie..you can buy like SLJB on Scottrade but they have a list of 2 dozen that you can only sell or not even buy or sell..
I asked David Braddock at Chattanooga office why?..and he said those stocks deal with clearing houses that do not have the normal 3 day settlement time..some clearing houses go as high as 5~7 days for settlement time and they don't mess with them..
one off hand I know of is SEIH..for example..
the whole list of stocks is on the stock trade site.