I have a stokke crib (2 actually in use). Ds2 is about to outgrow the mini & Ds1 needs to go to the jr bed. I get sheets from stokke, and also I had ds1's bedding made by Bebe Chic, so I had matching sheets.
My MIL easily made regular crib sheets into sheets to fit the full sized stokke crib mattress, so if you know anyone who sews, that's a good option. Honestly, now that ds1 is older, I have put a regular crib sheet on it and it is fine. I'm not worried about it coming up like I would be with an infant.
Have you looked into sheets by the few companies that make stokke bedding?
I have an unused, custom made mini sheet.
Definitely check etsy & custom seemstresses. If you have one sheet, someone could "copy" it for you.
Big Brother 5/07
Little Brother 9/09