I got mine about 2 years ago from Beech Vista Garden Centre Basic Sheds. They're at M50 Motorway Junction, New Ashborune Road, @ Coldwinters Cul De Sac (it's a big garden centre, and they also have a huge Christmas shop). Their telephone number is 834 2953.
The shed was great value, and I'm delighted with it. Have no connection with them other than as a satisfied customer who is pleased to recommend them.