Where did my buckets come from ?

They are 67 to 69 style Mopar seats, looks like they have been recovered in a non stock pattern. You can have them recovered in 1968 upholstery and they would be correct for your car. I'm not sure if 68 270 darts came with buckets or not, my brother has a 68 270 that came with a bench, but he's going to use super stock seats.