I would imagine that the BAR could very easily depose MN. he is a respected member of the bar in good standing who has had direct non adversarial contact with JB, yet has not been under any contracts or agreements with JB. So he is not bound by any priveleges. Remember MN worked for the A's, NOT KC. It has long been speculated that a major reason for his departure was they were expecting him to act in KC's interests and not G and C's. MN could and probably would freely answer any and all questions the bar puts to him regarding what he witnessed of dealings in the KC case, so long as it does not directly relate to his clients G & C. he probably has a strict obligation to do so as a member of the bar.
One other thought regarding JB's mysterious non profit charities. Does anyone know if any tax documents have ever been filed for them? Non profits and not for profits have much higher tax filing requirements, and much of those filings are public record. A non profit cannot have secret or private income. By its nature it must be subject to some degree of public revue. While you would not be able to get detailed accounting, you could at least determine if they filed in any of the given years, and what their rough net worth of income and assets were. To be a non profit and gain the tax benefits, you have to be willing to publicly say what you are doing with the money.