You can buy a new lens in MPH. Vendors have them.
Just about any Thunderbird with a manual shift is rare. One with overdrive is even more rare.
The '56 T-bird would be a great car to restore because it has a full frame. Most all the panels are available, too.
I think the most uncommon parts are the 12 volt gauges.
1956 was the first and only year to use 12 volt gauges. In '57, Ford quickly went back to 6 volt gauges with a constant voltage regulator, and kept that scheme for decades. - Dave