Scrollbar search markers

My application (x-platform Win + Mac) has a very long DesktopListbox in its main interface. I have a search function in the app, and when you get search results, all of the relevant rows in the listbox are selected for you.

But I’d like to add little highlighted lines over the listbox’s scrollbar showing the scroll position of results that are currently out of view. If you use a Chromium based browser I’m sure you know what I’m talking about, when you search a page, your scrollbar shows you exactly where to scroll to:

I don’t even know where to begin with this. Any suggestions?

This is not very elegant and I would be curious to see if the community could come up with a better solution. Functionally, one could have a thin tall canvas immediately lateral to the edge of the listbox and draw positionally appropriate horizontal lines across that canvas to indicate the location of “hits” in the listbox. (or even little arrows pointing left in the canvas acknowledging the fact that it is not directly over the scrollbar). You could jazz it up a little by allowing the user to click on the lines in the canvas and having the listbox scroll to the equivalent location.