Non standard mattress depth which there os no linnen available for.

I recently purchase a Restonic King base set from OK Parys. Got no guarantee documents or even a users pamphlet. Now I can not find linen that fits the 40cm deep mattress. I contacted Coen Myburg and Dale from Restonic after they returned from holiday and I had to prompt them again for a solution. They referred me to shops that I have already tried to source the 40 cm depth linnen. How can a company supple base sets with dimensions which they do not test with the linnen suppliers.