Who issues a certificate for any of the IRSA classes?
The certification authority issues the certificate. As of 1st July 2016 all the IRSA classes have the same administrative section. It is A.9 that indicates it is the certification authority that issues a certificate.
The term 'certification authority' is defined in the ERS as:
For the hull: the ISAF, the MNA of the owner or their delegates.
For other items: the ISAF, the MNA of the country where the certification shall take place, or their delegates.
The members of IRSA are the bodies to which the administration of RC sailing has been delegated (if not the MNA of the country itself) and which are known as the DNMs. So, for the hull it is the IRSA DNM of the owner.
For other items it will usually be the same but it could be the MNA or delegate of MNA in another country where the emasurement took place. This would apply where, for example, sails were certified in house by a sailmaker who had been delegated the authority to do that.
See also the related Q&A concerning who is the certification authority, or DNM, for an owner.