When I need to make a different fork spring spacer I use PVC pipe because it’s inexpensive, easy to get, easy to cut, not effected by oil and is much stronger than it needs to be.
This picture shows a PVC spacer next to some stock plastic, aluminum and steel spacers.
The stock plastic spacer on the right has a wall thickness less than half the thickness of the PVC pipe.
I made this post because a few people over the years have been surprised when they found out about the PVC. If the idea of a PVC spacer drives you crazy just let me know and I’ll be happy to use something else.