An easy way to set up a necropsy here in the US is to talk to your county extension agent. They will at least know who to put you in touch with. Many states offer this service free of charge of for a fairly small fee. The idea is to help prevent chicken diseases from spreading plus you know what you are dealing with if a chicken dies. It pays for itself by helping keep the state’s poultry industry in business so taxes keep coming in and people keep their jobs (the states with big poultry industry are usually the ones where it is pretty inexpensive) plus it can be a big help for us non-commercial people with small flocks if we are battling something killing our chickens, like a disease or something like that.
In a necropsy a highly qualified person cuts the dead chicken open to determine what killed it. Was it Marek’s, fatty liver syndrome, or some other disease? Did they break their neck or somehow injure themselves? Did they swallow a tack or screw that punctured their gizzard? It can be a huge benefit to know what actually killed the chicken so you know if you need to change some of your management practices or otherwise deal with it.