Hi Khaled,
While they used to be available as individual layers or toppers several years ago … unfortunately I don’t know of any current sources for 7 lb or higher memory foam any longer.
I would also keep in mind that once you are at about 6 lb density or so with memory foam that any additional durability benefits for higher density memory foam would be minimal.
I know you’ve already checked most of these companies, but there are a few extras on the component post #4 here.
I hope that’s helpful.
Phoenix