3dWarp has the option, -tta2mni, to transform a dataset from Talairach to MNI spaces. You can also use the MNI-space atlas datasets that are distributed with SPM, FSL, MNI or the Zilles-Eickhoff groups.
3dWarp -tta2mni -prefix amy_MNI 'CA_N27_ML::amy'
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