How Would I Get A Modern Diplomacy -"Like" Game Produced?
A few immediate thoughts:


from a game play standpoint where are the "BRIC" countries (Brazil, India, Indonesia etc) or are you designing the game to largely involve conflict between the 5 powers you cited in Africa, South America etc? 
from a "how do you get a game produced" there are many routes. An increasingly popular route would be to go independent - many games are starting with Kickstarter campaigns (where the supporters get the first copies of the game) which has the advantage of helping you gauge the actual market interest and demand. In the case of a modern update to an older game you may have to determine what, if any, patents or other IP rights you might have to license from the original (if any at all) and thus may have to deal with the original publisher (or who ever now owns the rights to the game). Since Diplomacy is a fairly old game it is likely that any patents on the game board etc have long since expired.
a final suggestion, Diplomacy has had a very long standing tradition of being played online (via email, via websites etc) could you make a digital, online version of your game before you make any investment into a physical game (with all the production costs &amp; distribution issues that involves?). A digital game, especially if you can attract a core of engaged players, likely would also help you iterate on the game design and evolve the gameplay and game balance based on many rounds of playtesting. 


And finally while there are game players here on Stackexchange I assume you do know about the very active and engaged board game community of BoardGameGeek? I'd strongly suggest reaching out to serious Diplomacy fans there and at reaching out to independent game publishers both on BGG and via their Twitter and websites. I'd also suggest subscribing to great game design podcasts such as Richard Garfield's great podcast (and there are many other board game related podcasts that feature long interviews with game designers and publishers).