There are many coon squallers out there, each of them produces a slightly different tone of squalls. Personally I use the Zepps Life Time Coon Squaller.
When trying to produce realistic coon squalls all you need to do is to flutter your tongue. If you can remember back in the childhood days when you use to make a machine gun sound with your tongue, it’s the same thing when using a coon squaller. So you need to flutter your tongue and at the same time be blowing into the squaller, just make sure you are blowing into the right end of the squaller. I like to cup my hand partially over the end of the squaller and then moving my hand around changing the volume and sound, giving it a realistic sound. Just try to imagine what a coon sounds like when fighting. If you keep practicing until you get the right sound you will find way more coon in those trees when the leaves are on. Also, another tip while squalling, use a low dim light or ideally red lens on your light, a coon will look at a red light quicker than a bright white light.