For our humanflows visualization, we used data from the United Nations Common Database and the Migration Information Source. The great thing about these types of sources is that they are publicly available so that everyone gets to have fun with the data. The downside is that the data is accessible via a user interface that often makes it a chore to get all of the data.
Hence, to save you some time, you can now download the migration database that we used. I don't see any reason why you have to go through the whole data importing process when we already did it. Enjoy!
Disclaimer: Keep in mind that the data is from the United Nations and Migration Information Source, so you should refer to the two sites for any documentation. In a nutshell, the inflows table is from MIS and the rest is from United Nations. If you're looking for more, you might also want to check out OECD. I really wanted to use their data at the time, but was having trouble accessing it from Spain.