Senior candidates are very comfortable with their current job. Why?

Use linked in to find suitable candidates, look at there history of employment;

Are they adventurous, do they have a tendency to relocate across SE ASIA and beyond. Is there a pattern to their employment duration, do they have a family and therefore likely a settled life in thailand ( not easy to move if so) do your homework on every candidate prior to the call so they know you have screened them for suitability, keep the call for what it is just a call and intro. Invite them to view your website or information do not request email as too many scammers, opt instead for a different option like whatsapp/line ID group which gives updates on opportunities if there interested then that's how you track them by there own admission to joining the group. Why not initially target middle managers who will be more interested in taking the step up and likely will have trained under the director and once you see the process working and your script is sharp, then target those top execs.