Do you have Hehr or Kinro windows? I would contact whichever company and see if they can sell you just that part.
If they don't help you, you could try an RV dealer. They will have to custom order that part, I guarantee you, but they might be able to get it alone.
The only other suggestion I have is to see if a dealer has done a warranty repair on a window (if it leaked, etc), if they are scrapping the window, maybe you could get a latch off one of those.
Hehr: (574) 935-5122
Kinro: (574) 535-1125
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR