Where can I find a large duckboard????

Hi ladies, any ideas? I have been searching for a large, pref white duckboard for the shower, but can only find small oness . Need 70 x 100 cm. Have tried bathroom supplies, M&S, Dunelm and all the usual ones. Can only find a ' bespoke' at £190 - I thimk not...

Or should I just have one made?

Thanks, Genie

Where can I find a large duckboard????