You can take them to an avian vet, but that would be expensive. If you have an agriculture college nearby, they will often test them for free. We are close to University of Florida, and they will send someone to your house and test for you. Some vets will do slides for you without a full vet visit, you would have to call around and see what they can do, and some states will have state rep or county reps that will test for you. You could call your local extension office, they would often know who can do testing in your area. I know that isn't much help, sorry! Respiratory diseases can be very tricky, i had a friend we were sure her flock had coryza, testing showed it was MG.