Is seems NOAA actually has geomagnetic indices here and in
principle you could download it and even look at a GIF animation, however I always get the error message:
SPIDR cannot execute the requested action...

Potential reasons:

If you're using Web Services, please confirm you're using correct parameters and arguments Web Services Guide
SPIDR may also be under heavy load, if you feel certain your request is correct, try again later.

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Anyways I haven't even found an official definition of the aa index. The aa index starts in the 19th century, while the K and ap indices only in 1932 according to the NOAA page.
It's also not explained here.

The aa.doc in doesn't say at which time of the day the three-hourly measurements start.

all this is annoying.