Nope! Been to B&Q and the like and they tend to sell lots of pvc doors and standard wooden external doors. I'm after the cottage style traditional stable door.
If you can't get them from either of the above DIY sheds, you will definitely be able to get them through any Builders Merchant (Travis-Perkins, Jewson, Buildbase - ther are lots of national ones around). They may have to order it but it will take only a few days.
When you get one, think carefully about the placement of the locks and catches. I had a stable type front door as an unusual birthday present, and it came without fittings.
You have to have a way of closing the half door as well as the whole door, plus a catch between the two, otherwise you can'tmake the most of the possiblities.
Have fun.