Oh most of us that change it so often make the icons ourselves.
If you ever find an image you want to be an icon I could always make it for you. XD Ive made probably near a thousand or so icons by now. I really enjoy making them
But essentially you search up whatever you want an icon of, you find an image that you think would make a good icon, take it to some kind of editting software (or paint if you dont plan to do much to it), and at the very least, crop the image to be the size you need it to be (square)
You can get more creative with it the more your practice too
I usually used
link to edit and crop and all cause its like Photoshop but online free and has no downloads. Not as good as Photoshop but definitely plenty enough.