The radiator support is not a bolt in item. Replacement radiator supports are available from several companies, I know Mustangs Unlimited sells them, I believe at a price of $150 or so, but you will need to verify. To replace, you must remove the front clip, front fenders, radiator, headlights, and anything else attached to it. Cut out the damaged radiator support and weld in the replacement panels. I would definately order in the new radiator support before you start cutting so you know where exactly your cut lines need to be for easy re-installation. This will be quite a large job, you may be better off having a shop use a hydraulic jack to push it back to where it will at least hold the radiator in the right place. This job of course will require some form of a paint job on the affected areas to prevent rust as well.
Certainly not the job for an amateur, if you have any doubts, a good body shop should have no problem repairing this. If you have any further questions, please let me know.
-KB