Reference - Freight Cars Journal #15 by Eric Neubauer is the reference for carbon black cars like these. “Columbian Carbon owns the second largest fleet of carbon black cars.”

Suitable Models - Scale Trains has produced HO-scale 5750 cu ft Thrall covered hopper models.

Social Media - The Rail Car History group on groups.io is a good place to start.
https://groups.io/g/railcarhistory/topics

Properly stored, these decals should remain usable for many years.

Acknowledgments - Special thanks go to Susan and the late Wade Griffis, of Jenison , MI, Society of Freight Car Historians, and Ron Roberts of Rail Graphics, without whom this project would never have happened.