They obviously didn't integrate him very well. I assume they probably just tossed him in the yard and left him alone. That's not the proper way to integrate new chickens, and it's no surprise that he got beat up.
There are many knowledgeable people on here who would take great care of your rooster. I'm sure you could find someone who would take him.
Or, you could go to your neighbors and ask if they would allow a rooster.
I'm sorry if my post offended you. I did not know that you already tried to rehome him and it failed. But, I still don't think decrowing is the right thing to do. The surgery is incredibly dangerous, and expensive. There are other solutions to your problem that are a lot less harmful to your rooster.