MS Access: Capture ListBox Scroll Event?
There is no such event handler available in Access.  Access controls are very limited compared to, for example, the .Net counterparts or other development environments.

I can't disagree with using "built in routines", but even if the scrollbar did expose more events, you'd still be trying to force the listbox to behave in a non-standard way.  Especially in Access you'll have better luck implementing something with specialized buttons as you've already mentioned.