This is not a plugin - it is builtin into the AFNI code. It is available from the right-click popup menu in a slice image viewer window - with the mouse cursor over the slice image, press and hold down mouse Button 3.
However, you must have the TTatlas+tlrc dataset stored in the same directory as the AFNI plugins and binaries (i.e., in the AFNI_PLUGINPATH directory). If you don't have it, then you can download it from [
afni.nimh.nih.gov], among other places. You will need both the .HEAD and .BRIK.gz files.
bob cox