In the US, its very rare to need health certificate/vet inspection at shows. The only time I needed it was a non-sactioned show (not any association) and it was strickly household pets.
They do state that your cats should be up to date on shots, but never ask to see proof. If someone suspects your cats are sick, then you will be asked to leave and take ALL your cats with you. I've only seen that happen once or twice in all the years I've shown.
Now over in England, etc. they DO require a vet inspection and probably shot records at their shows.