How do I get a power of attorney for a deceased husband?

Sorry. Only a living, competent person can issue a power of attorney. In California, there may be an available alternative to a traditional probate case if the total estate is less than $150,000, or if all the property was community property at the moment he died without a will. Otherwise, a probate case is necessary to transfer property that was not owned in a trust, in joint tenancy or for which an effective beneficiary designation was made. The estate attorney can make a determination what procedure, if any, is appropriate and available.

You can not get a power of attorney from someone who is dead. Look at the Nolo Press book available in your public library as to what you can do.

You cannot. POA are for use during life. You must rely on estate planning measures. If your husband did not have a will then you must seek to be appointed Administrator via Probate Court.