Keep an eye out on eBay. I found a NOS one for my ‘65. They are not easy to track down, and not reproduced…add it to the long list of Galaxie parts that are getting harder and harder to find.
how bad is your original? Mine had one crack in the upper part that really wasn’t very noticeable. The one I had could be glued if just needed something in there.
Here’s my NOS lens in place on my restored shifter, and a before pic of the unit. I believe the part is the same for ‘66 even though the C6 came about, as the the shift pattern was the same.