Hopefully someone will understand what I mean

When I pull out the headrests, there are obviously two holes left in the top of the seat. I have ONE little plastic insert that fits perfectly but the other has been lost - any ideas where I could find such a thing? Or even what it would be called...
Much prefer the look of the car with headrests removed, much like the sidescreens I just use them for touring now.
Help pleeeeease!