Those looking for treatment should seek out providers who offer cognitive-behavioral therapy. They should have experience with exposure and response prevention (commonly used for OCD).
Dr. Kiara Timpano (University of Miami) is a wonderful colleague who does a lot of work with hoarding. She has excellent doctoral student trainees who would be a great low-cost option for your clients (they'd be low cost and much more experienced than most general providers).
https://my.clevelandclinic.org/health/diseases/17682-hoarding-disorder
https://www.mayoclinic.org/diseases-conditions/hoarding-disorder/diagnosis-treatment/drc-20356062
This website is a sister site of the International OCD Foundation. It should provide a lot of useful information, and it also includes a resource directory where people can search for individuals experienced in treatment for hoarding.