The U.S. Commercial Service, American Embassy in Bangkok has resources Government Tenders that help identify promising leads for U.S. exporters.
You can search leads notification when new leads are posted per below;
1) Asian Development Bank (ADB) Projects and Procurements Notice for Thailand
2) Electricity Generating Authority of Thailand Procurement Notice
3) Metropolitan Electricity Authority
4) Electricity Generating Authority of Thailand (EGAT)