Where can I open a brokerage and mutual fund account for investment in Thailand with DTV?

Who is advising you ?? Why would you do it inside Thailand, given that this will make it subject to capital gains tax at income taxation rates in its entirety.. When you can do it offshore, hence not be subject to capital gains unless remitted to Thailand ? Thats without getting into the higher expense fees and maintenance costs of Thai brokerage houses.

Interactive Brokers and IIRC Blackrock are some of many global brokerage houses that allow Thai residential account opening. Vanguard doesnt IIRC.