I would never show a sick bird! Let that be said first and foremost.
Ok, I decided to talk to about showing and coryza too.
I honestly don't see a problem. Here's why:
A number of show folks that I know vaccinate their birds for coryza. This is done all the time. There are two types of coryza vaccine: one is a live virus the other dead. It is the live virus type that is the most readily available and used. Once vaccinated with the live virus that bird is now a carrier!!!! However, these birds are shown all the time: particularly in the northern states. Just go around the show room and ask.
Any bird that has been in the presents of a bird with coryza is a potential carrier as I understand it even if they have never shown any symptoms of the disease. In other words, it's as if they had been inoculated. I see no difference between the two.
That said, if someone ask me if I've ever had coryza the answer is yes. Where did it come from? Wild birds? The Show Room? I don't know. I just know the reality of fighting the disease.
By the way, all the people I know really well that raise and show birds have also had coryza. As a matter of fact, most of the free-rangers I know have had it too. saladin