Lid for Really Useful Box 20/33/50/64/84 litres (IP4)

I have a 64L Really Useful Box which unfortunately has no lid. The RUB website indicates that the same lid is used for the 20, 33, 50, 64 & 84L boxes.
New lids are reasonably cheap - under £7 each - but there are two problems: (i) the minimum order is three, and (ii) they are out of stock anyway! So if you have a spare lid lying around, it would be much appreciated. Thank you.