Where can I get I kids book called "Kathy & Mark"?

I am looking for a present for my sister, it's one of my earliest memories, me and my sister laughing at this book called kathy and mark. It's just about the two of them doing really simple things. I think it had an orange cover. It would mean the world to me if I could find it. I suspect it isn't published for a good while. Problaby like 12-14 years ago we read it. Any ideas?