@anita0524 If you are referring to the disorder known as hereditary brachial plexus neurotic, there is a clinic dedicated to this rare disorder at the University of California San Francisco Calle the Brahial Neuritis Center. Have you tried looking their website for information?

There is also a brachial plexus network at the National Organization from Rare Disorders:
https://rarediseases.org/organizations/united-brachial-plexus-network/
As to stem cell treatment, this must be highly individualized to the person and disorder, so any search for a Practitioner should start with one of these organizations.
Other "Stem Cell Clinics" not affiliated with a research organization are literally taking a very expensive "shot in the dark" at this point in the development of emerging therapy. Those promoting embryonic stem cells have been issued warnings or cease and desist orders by the FDA. To date the FDA has approved specific stem cell therapies for about 80 conditions, but I didn't see any neuropathy conditions listed (yet).
Does your husband's inherited disorder have a specific name you can research?