What is the general success rate of Rabies Vaccination of adult healthy cats when it comes to reaching an antibody level of 0.5IU/ml 120 days post vaccination ( for approved international travel ) ?
No one on here is a vet, so they likely don't have access to those studies.
Two things you can try to get an answer to your question:
Call a veterinary school. See if someone there has quick access to this.
The other option is to find out the manufacturer and type of vac used and call the manufacturer. This may be the easier of the two solutions.