How to advertise an academic job in a small Asian country to US/European candidates?
Try conferences. I'm not in math but in my field most of the job news comes via conferences and academic societies.

It helps if the jobs are for specific subfields, so you can advertise them to the smaller conferences/societies for those subfields.

You may also try focusing on conferences/societies outside of the US, like Australia, NZ, Canada (e.g. Canadian Mathematical Society). Jobs in smaller countries like Canada are harder to come by and people on the market might appreciate seeing other non-US options.