Did a quick browse on Ebay and my local Craigslist for the item, and didn't find anything, and Im not really well versed in the part you are seeking.
I am familiar with modern software defined radio and other radio techniques. Id imagine there would be a setting somewhere in the preferences to change region to US. otherwise, It is possible to build a device (called a downconverter) that shifts a 90-107MHz spectrum down to the Japanese FM radio band. on 76-90MHz.
I found a commercial model downconverter on Amazon that looks like it would work if you can't switch the tuning range in software. Some cutting and wiring will be nessary, but all outside the mac