As Hamish says, Club Kilts make a Saltire Kilt which, from memory, is a plain blue kilt with a altire on the front (can't recall the back view).

However, there is an earlier version available from some kilt shops with a newly invented tartan called Saltire of Scotland - essentially blue with white vertical lines - and in a triumph of the kiltmaker's art they have managed to pleat it to line into a Saltire at the back.