You may be able to find a good avian vet with poultry experience (rare as hens' teeth) that would do it but even they probably don't have the tools on hand.
Caponizing kits are available lots of places online.
https://www.meyerhatchery.com/productinfo.a5w?prodID=CK
https://www.themodernhomestead.us/article/Caponizing.html
It would probably be easier to do it yourself than it would be to find someone else to do it.
There are commercial poultry operations where they do caponizing but I'm sure even they don't do it regularly and they wouldn't allow someone to bring in an individual bird for the procedure.
Why do you want to caponize. Is it to keep a rooster from crowing or to get him to grow larger for slaughter?
The terminology for neutering males is different according to taxonomic class.
Neutering mammalian males is castration.
Neutering avian males is caponizing.