Where can I find statistics about international movement of students/academics? I am wondering where I could find global statistics on the flow of students between countries. This would include numbers such as "how many students with US bachelor went to UK for a master" and "how many Spanish master students went to US for a PhD"

They always say that the academic world outside US suffers from brain drain towards the US, i want to find way to quantify this
I don't have the statistics at hand for the case of students. But there was recently a publication of mobility statistics for scientists on 16 countries:

The report is here 

The IEEE also made an infochart that was a bit more explicit using some of the data in the report.