K&S metals sells a Phosphor Bronze sheet. .008 thickness. You can cut it with scissors. I’m no expert on this. But you want enough tension to make a good contact but not so much that the wheels won’t turn. You will experience some drag no matter what you do. If it’s easier you can also go to the backside of a wheel. The only trouble with the sheet as they can be pricey.
Tichy Train Group sells it rod form. I believe the thickest is .040 . I would probably go with the thicker ones seeing it’s not a flat surface and you may need that extra tension.
What is it your working on ? I recently added different trucks to a caboose that were 3D printed. I used the factory Lionel ground strap and added a few bends to it and some mounting holes. It rides on the backside of the wheels.
