What is the name of this part of an old window?

I am in the process of restoring old windows. These are original to the house and hence from 1940. Windows have these plastic or metal ventilation plugs, here are two pictures:

The problem is some of the windows miss these parts, and I would like to replace some of the older ones. I, however, have no idea what these parts are called. I tried to google some random terms (such as vent plugs for wood windows) but did not find anything.

So, what is the official name of this part? and it is possible to buy a replacement?