I have been to my nearest "big" auto parts store on Sukhumvit soi 56 but they only have "standard" parts. Ie. plugs for standard cars and I need one heat range colder than stock.

You might try this place.

http://www.asianconceptthai.com/product--736-1.html

I have the same problem here they don t have higher then the series 8 while NGK also has 9 and 10 series for fast 2 stroke engines.

Solutions order online or ask a friend from other country to buy and send them.