If you don't have an Owner's Manual to look up the lamp number, you can get a PDF at NissanUSA. (If you plan on doing any work on your Z, the FSM is a great resource. Link in my sig.)
More than one thread on the subject of lic plate lamps; at least one link to a vendor. If you don't like the site's search, go to any search engine and add "site:the370z.com" to your search string. Eg,
https://duckduckgo.com/html?q=license plate lamp site:the370z.com