Here's everything you'd need http://www.pets4homeopathy.com/remedies.html
It's all homeopathic and has mixtures of herbs, in clear, odorless, tasteless liquid. Don't waste your time giving just one herb or two that you heard will work, etc. I did that and got no good results, use these pre-mixed formulas.
You should also use the DETOX one in conjunction with the one for respiratory. I don't think they have one specifically called RESPIRATORY, but the one for SNORING I believe is basically all the same herbs for respiratory problems. Also the one called INFECTION is good too. And it wouldn't hurt to deparasitize your pet too. Get the one for parasites it's called Paralixer. They are all herbal remedies.
Just put 4-6 drops in 2 cups of water (their water dish) for 30 days. You should see some improvement within the first week. Try to find a formula that applies to the symptoms your pet is having and ALSO get the detox and infection one. If your pet hasn't been dewormed in a couple years, DEFINATELY get paralixer. Animals should be wormed once per year and more than that if they live in multiple animal homes, 2x per year, 3x if in a cattery or kennel.