MichaelBevan
Should be able to find some replacements on amazon, but as for a CMF replacement, I am not sure. Amazon seem to have a good selection from fitness to stylish bands. What you need to look for will be a 22mm Quick Release Watch Band. Take a look here.
OliwierKaminski
When I purchased my Watch Pro, I also picked up this: MIHENCE Compatible for CMF by Nothing Watch Pro Screen Protector and it was pretty cheap. It was not the easiest to apply, but it did come with 6 of them, so if you end up screwing one up like I did, you have more haha. I have found it to be perfect for what I was looking for. If you are familiar with PPF (Paint Protection Film) it seems like it could be the same material. I have bumped the watch face on a couple of things, and the scratches “heal” themselves. Although I am sure if it was a hard enough scratch, it might go through the protector.
Not sure where you are in the world, hopefully this helps!