For engine parts for the Yamaha Touch 125 and VR150 you best can contact www.akunar.com in advance. It's unlikely that any regular dealer in Thailand has stock for motorcycles like this they're just to old.
The problem with the Yamaha Touch 125 is that it was never officially sold in Thailand. You probably have much more luck trying to find parts in Indonesia.
The Yamaha VR150 was sold in Thailand as the TZR150, you can still buy original parts from any Yamaha dealer in Thailand. But, I don't know any Yamaha dealer who has parts on stock... parts are only available via special order at the factory/parts distribution center.