I am a law school graduate. WHat I offer is mere information, not to be construed as forming an attorney client relationship.
Well;, start with your contract with them...are any non compete clauses in there? If so, you may be out of luck.
If there no non compete clauses, companies build what is called goodwill and that is something that can be quanitifiable.
What lawyers do in law firms when they strike out on their own and want to bring those clients with them is they issue a letter to their clients. I am not sure when they do the same with the law firm.
That way, the client gets to decide whether to stay or go.
Speak with a medical supply board or organization, if such exists and see what they say.
Hope this helps.