The archive containing all these standard data and associated files is available from the ADNI website (login to ADNI, follow Download -> Study Data -> Test Data -> Data for Challenges -> "Tadpole Challenge Data"). You will need to
register with ADNI and apply to access these data files. In the archive, the file D1_D2.csv contains both data sets D1 and D2, with row-wise membership indicated by a 1 in the "D1" and "D2" columns, respectively. The file D3.csv contains D3.
That's how I got it.