We have misled you in our previous reply. Basically, the suggested approach was for WPF and you marked this ticket for Silverlight. The reason why you can't find the Thumb and get null is that the Loaded event is fired too early and the control template is not yet updated. In this case, you can subscribe to the LayoutUpdate event of the RadTileView control.
As for your question, scrolling the tile view per item while dragging the thumb won't be an easy task. Basically, when you change the position of the thumb while dragging in order scroll per item the position of the mouse will not correspond to the thumb position and you will get unexpected behavior. An approach which you can try is to implement custom ScrollViewer where you can create custom logic to scroll the tile view per item using ScrollToVerticalOffset()
method. As for the mouse, when the dragging operation starts you can hide the mouse cursor and show it again when you operation ends.
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