I am sorry to say but I could not find any musically tuned bells that would fit onto a cats collar. They do make musically tuned bells but they are much larger in scale and they are hand held and the cat could not withstand the weight of the bell. They make windchimes that are tuned...but I am afraid those will also be too heavy.
I would suggest putting different types of bells on each cat. You can use tin bells (like a cow bell in small version) on one cat, mini chime on another cat, jingle bells on one, etc. I found a website that offers many different types of bells that come in different sizes. The sounds should vary slightly due to the dia. of each of the bells. The smaller the more high pitched. The wider the mroe hollow and deep the bell ring will be. There are several different bells on this webpage and I think it will be a good solution towards what you are looking for.
http://www.ajantaenterprises.com/bells/bells.htm
If you have anymore questions, or want me to research more into different types of small bells that could make differnt noises I would be happy to do so. Good luck!
Maggie
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