None off Ko Tao either ... I got dragged off on a big game fishing trip and only caught tiddlers. Waste of money, would have been much better spending my 1200B on a much needed spa treatment. I went night squid fishing recently though and caught some of them.
The only place I have seen black marlins, blue marlins (and 13m whales) in Thailand is the around Surin islands. It's a national park and big game fishing is prohibited there which probably explains why I saw them.