#1: Where do you live? A country or continent is always helpful.
#2: Pacparts.com is a great resource of all Casio and G-Shock parts -- their database is often extremely helpful. Unfortunately, they show the MTG-510 module as being discontinued, but even if it hadn't been discontinued, Casio apparently decided about a year ago that they would no longer sell modules to the public -- instead, all newer models show the module as "restricted part, contact factory service center."
#3: Based on that latest change, your best bets for a replacement module are probably your local Casio service center OR the used market, especially eBay.
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