You'll need to use saveAssociated
to solve this, but if your tables are not exactly the same then you will first need to transform your data into something manageable. Here is an example:
$table_1 = $this->Table_1->find('first', array('conditions => array('Table_1.whatever' => 'something')));
// here you can manually build the data you need to save.
$transfer_data['Table_A'] = $table_1['whatever you needed to change'];
You might need a for loop or something to convert your data to the slightly different version that you need for table a and b, but without knowing what the difference is there I cannot write the code that does the transformation. Once the transformation is complete you can just save your save as explained in the manual using saveAssociated
.