Where are AA / supersampling controls in C4D?

Unlike most renderers, Corona does not provide direct control over maximum or minimum allowed supersampling / subdivision of pixels. 

Generally, within one render pass, one AA sample is cast per each pixel. This is a simplification, and the process is really a bit more complex because of adaptivity and other features, but we can assume that the total amount of AA samples per each pixel equals the amount of passes used to render the image. (e.g. after 16 passes each pixel has received 16 AA samples) The only way to control final amount of supersampling is by stopping the rendering after desired amount of passes or by defining a pass limit. To render more passes in the same time, thus focusing computing power more on anti-aliasing than on GI-sampling, you can decrease values of "GI vs. AA balance" and/or "Light Samples Multiplier".

You can also select a specific image filter type and control its width. You will find it in Render Settings > Corona > Frame Buffer Settings > Image filter. Setting image filter to "None" will not disable anti-aliasing.

Note: it is recommended to use default settings of the image filter for best rendering speed and quality (type: tent, width: 2px).