>What I thought I had seen at one point was a ComboBox, style=Dropdown List. If you clicked the down arrow, a list of items defined in the rowsource would appear along with a scrollbar on the right. As you dragged the slider bar down, the values being displayed would change in accordance to the position of the slider bar.
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>Right now when I click on the down arrow, I get a list, but I can only scroll the list by making single clicks on the up and down buttons, or dragging and releasing the slider bar.

Now I understand what you asked for. Unfortunately, I have never paid attention to this minuscule details. Basically, it's not a purpose of combo to provide specific scrolling, because combo should be used for small number of items, i.e. user will not have a chance to see any difference. Use grid if you want to give user ability to select from hundreds (or more) items, and/or educate them to use InteractiveSearch.