U can get 225/40/18 tyres from Hua Hin Tyres & Services in Sg. Besi area. I'm using the same tyre size for few years already & the price differs from the brand that u want. The following below are the prices I paid for different brands for the same size:
1. Dunlop Direzza DZ101 (Japan) - RM580 each
2. Pinso Tyres (Indonesia) - RM310 each
3. Dunlop Sport TT Maxx (Japan) - RM730 each
4. Yokohama A-Drive R1 (Philippines) - RM330 each
5. Continental Sport Contact 3 (Germany) - RM830 each
So these are the brands that I've used before for the past 4 years until now. I changed my set of tyres every 9-12 months depending on how much I drove.