I would isolate all the show birds from the rest of the flock; however, I would recommend treating all birds since all have probably been exposed.  Birds drink, trichomanids enter water and other birds are exposed.  The next time you show have a quarantine cage that you put the show birds in after bringing them home.  Quarantine just as you would any new additions to the flock.  With treatment, you can control this problem.  Just be aware that the flock may have periodic outbreaks whenever stressed.  I have pigeons, and it is pretty much endemic in pigeon flocks.  This year I kept my numbers low, disinfected waterers daily and had no outbreaks even though I know that my flock is infected.  It is an opportunist that strikes when conditions are right.  Yes, your birds were stressed from the show and may even have contracted the organism from improperly cleaned cages, feeders, or waterers.  Good luck.  You have caught this early and can resolve the problem.