Andersen window molding/glazing

We are trying to find replacement snap-in exterior grey/terratone glazing for our 1984 Andersen 400 series casement windows (fourth photo shows a close-up) and also replacement molding that appears to be made of plastic and is located between the fixed and casement windows in our home. The windows are placed very close together; this molding fills the space between them, as shown in the first photo. This molding is T-shaped; the third photo above shows the profile with most of the spine (which is at least an inch deep) broken off. I was unable to remove a piece showing the full depth of the spine. The second photo shows the molding in place with the top broken off due to weathering (southern exposure).

Thanks. Do you have any ideas regarding the T-shaped molding between the windows?