Anderson shelters occaisonally pop up on Ebay if you are really keen.

Anderson Shelter WW2 Log Store 8ft X 5ft | eBay
And it's been loosely to together just for the pictures. 8 panels making it just over 8ft long and. 5ft wide, or it could be used to make smaller units. Anderson Shelter WW2 Nice patena.
www.ebay.co.uk