I have only seen one. It's sitting in my garage !!!! I bought it from the original owner in July. It has 11,000 miles on it. They will be very hard to find. I haven't been able to find any production numbers but I was given a letter by the original owner that he got from Buick stating that there were 61 Buick Century Turbo Coupes built in 1979. I figure that there were even fewer built in 1980. If you find one, make sure it's in pretty good shape. All the exterior sheetmetal & the rear interior panels are special to the Century. If I come across another one, I'll let you know.
Good Luck !!