Hi ps99115,
Welcome to the Mattress Forum! 
While the focus of this forum is primarily on mattresses, I do have some links to sheets in post #7 here. Also, if you scroll down to the component supplier post here there are some companies who cater to more natural products and some of them may carry the types of sheets you’re looking for.
I’m not familiar with this brand, but perhaps some other knowledgeable members of the site might have some experience with this brand and they could comment.
Let us know if you end up finding something that you like!
Phoenix