Could probably get one 3d printed. The problem is that I imagine unless they are made specifically for that board (or even so) it may act as more of a heat insulator and prevent airflow over the main components of the board.
They claim to be specifically designed to allow heat dissapation. One in particular that I looked at had fans underneath the vrm covers and openeings that could be adjusted to suit. AFAIK they are a feature of specific boards, but I like the idea of 3D printing a custom cover. I do think that you would have to build a fan into the vrm housing as well, I just done believe convection would do the job appropriately