I bought rollers to have a test stand for HO engines. I bought a set of 4 and an additional set of 2 to cover both BB (4 axes) and CC (6 axes) engines. They are available at Miniatures Passion here, they come from DCC Concepts - link.
Let's see how it works:
The blue pieces without the wheels allow having a test stand at a different scale:
Let's see for a CC 40100 - 6 axes. This is Trix 22574: