I'm not sure about alternative discs for the X, I know a fair few bikes share the same (smaller) discs as the R and Z models. However, you should be able to get an EBC one shipped just about anywhere in the world, or alternatively there are Chinese made wavy discs available on ebay from Hong Kong, which you should be able to source from Cambodia.

Here's just one of many examples...

http://www.ebay.co.uk/itm/Front-Rear-Brake-Discs-Rotors-fit-for-Yamaha-XT-660-X-Supermoto-2004-2011-Gold-/170985812968?pt=UK_Motorcycle_Parts_13&hash=item27 cf8c73e8

Probably find cheaper ones if you search ebay properly, I just spent ten seconds on it!

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