The part I need is a Toro 88-9780 which is a steel ring in several pieces that bolts to the deck. I hit a rock and mangled mine. It is discontinued and no where to be found.

The mower is a 71182 12-32 XL Toro tractor.

Thanks!

I don't see it available any where..
 
If your slightly mechanically inclined, I'd remove what's left, take it to a hefty vise and go at it with 
a 5 lb ball peen hammer...
 
You'd be surprised how much you can straighten it out as it's not terribly thick..
Take your time...
 
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Thanks. I’d do it but it was literally torn off. Would need to be welded. In hind sight I should have done that and some hammering. I tossed it unfortunately. Cheers!

You can trace the deck (area concerned) on card board and then transfer to steel.
 
Use a Sawzall (or similar) to trim it to shape.
It would take some time but do-able.  
 
You could also bring your "template" to someone that works with metal to make one...
 
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That’s a great idea with the template. The whole mower should probably be replaced at some point. I’m not sure that it’s even worth it. I was thinking I could just operate it without the ring and be careful.

In the meantime, perhaps someone might have those parts. Thank you for your suggestion though. It makes total sense.

If you have your yard pretty much cleared of rocks, stumps, etc, I'd run it as is.
 
It does help the deck to last but the deck still has the curved / flat bottom that still 
has rigidity.  
 
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