My 2018 didn't come with dividers either. I spent awhile researching and never found anything. So I purchased some black marine grade moisture resistant HDPE and made my own.
https://www.mcmaster.com/9785T805-9785T312/
I made 2 prototypes using cardboard to get the exact sizes needed and then machined them at work. Here is how they turned out. You can also choose different colors if you want.
Each divider is a different size by the way. If you don't have access to machine them you can purchase 1/2 thick and cut out the perimeter only. Keep in mind the pockets these fit in are tapered due to the molding process. So 1/2 is tight at the bottom and 3/4 is tight at the top in my truck.
Sorry the last 2 images aren't better. I took pictures of the PDF's on my laptop.