ventilating window replacing non

I'd would look at the old window and at one of the corners in the glass you should see (maybe very small and hard to see tiny print) the maker of the glass and some other numbers. Those numbers will help you get the same tinting and color at a rv glass place, but with openings like you want. You also might see the manufacture of the frame of the window or window frame. Most window manufactures make their window frames common sizes the rv builder decides to put it, full glass, or partial glass, with or without sliders and which way sliders go.

resource for a window that would be a direct replacement

You might find many replacements after you have what exact numbers you need. RV dealers or on-line, but don't buy until you know exactly what you need for a replacement. One of the biggest suppliers is Hehr.

http://www.hehrintl.com/
Replacing a window "complete" is easy and many youtubes on it. But getting the frame with sliders that you want might be harder.