Does it fit a mountain buggy duet

Hi Sarah, thank you for your enquiry, we do have a Shade A Babe that would be suitable and is a universal fit. you can find it here: https://www.babyonthemove.co.nz/on-the-move-/sun-storm-covers/Outlook-Shade-A-Babe-Snooze-Plus?search=shade%20a%20
We hope this helps.  if you follow the link https://www.babyonthemove.co.nz/store-locations/ this will take you to our online store finder. Here you can find contact details for your nearest Baby On The Move Store 
 where one of our team experts will be happy to assist you in your product search and help answer any further questions you may have. We hope this has helped with your query.