Good advice from
@Eggcessive
NC also have 4 state labs - Raleigh, Monroe, Elkin and Fletcher/Arden, you might want to contact them to see if they can do some testing to find the cause. Ask them if they can accept swabs to test for Mycoplasma, Infectious Bronchitis and ILT.
http://www.ncagr.gov/vet/ncvdl/
Since he is a show rooster, I would not show him again until you find out more information since most respiratory diseases make birds carriers for life - you don't want to contribute to the spread of disease.
One more thing, if you haven't done so, I would definitely take a look inside the beak for any lesions, white/yellow patches, etc.
I'm sorry he is not well, he's beautiful. I hope he starts to get better soon.