mazda 6 not starting at all

Assuming I've read your question correctly, my interpretation is that you feel you need to replace the steering lock mechanism on the steering column, is that correct? If that's the case, the following section of the repair manual will show you how to do that replacement.

Steering Column: Service and Repair — 2008 Mazda 6 L4-2.3L Service Manual - Operation CHARM

My problem is that the column lock doesn't have anything to do with whether you can start the car or not; that should be a function of the ignition switch itself, rather than the steering lock mechanism. The following page shows how to remove the ignition switch without having to dismount the steering lock.

Ignition Switch: Service and Repair — 2008 Mazda 6 L4-2.3L Service Manual - Operation CHARM

Although I randomly selected the L4 engine vs the 6 cylinder since I don't know which one you have, the procedure should be the same; you can always navigate to the appropriate page on the 6 cylinder guide if you want. The preceding pages also have troubleshooting and testing information to help confirm whether the parts are working correctly or not.