You do not have to have a peafowl or any type of fowl expert to be able to do a fecal float exam. It is a common procedure for finding the eggs in the stool of dogs cats, and other pets. Call around to any regular vet, a farm vet would be best but ask them if they do fecal floats and how much they charge, they should be around twenty dollars. Start with collecting fresh droppings from a number of your flock, a pea size from eight to ten different stools is recommended.
I have been through hell this year with my peas and I assure you that you need to know IF there is a worm load (and what kind), or IF you have Coccidiosis that need to be taken care of or you will never get rid of the secondary infections that came along with the worms.
It is probably too late to do much of anything for the stricken pea but it is not too late to save the rest of the flock. Once you know if you have worms or cocci then you can take on the respiratory infection. This is not a recommendation on what to do, but, the best results I had clearing it up was daily injections for three days of 1 ml Baytril and 1 ml Penicillin. It is called a duplex shot, meaning that both meds are in the same hypo and given just under the skin at the base of the neck.
To keep from stressing your birds any more than necessary have a helper. Catch the bird by penning it to the ground, find and extend the legs straight back with one hand and hold the bird down by placing the other hand on the back. Then you can use both hands to pinch and pull the flesh up with one hand and insert the needle with the other. Aim the needle from back to front to more easily find the skin and avoid piercing feathers. Do not dally, get it done and the bird released asap. When done hold the bird down and back away, usually they will lay there until the figure they are free and get up slowly. It is very easy to go through both sides of the skin and completely miss the bird, be careful that the needle tip is still inside of the bird before injecting the medication.