Hi Maryanimal,
I spent some time looking at their website and I added London Bridge Linens to the reference post here for mattress encasements (they are the only one I’m aware of that can be custom sized) and also to one of the reference posts here for sheets and bedding because I saw that they also make custom sheets in any size and shape including split king sheets.
Thanks again for the heads up and for letting us know about them 
Phoenix