So, I made my own, now available for public use and plagiarism:
|Click to embiggen, save to save.|
This is a very rough, rushed version, with as few details as possible. Consider this a template for anyone to borrow and improve on however they need to. For my grade 8s, for example, I plan to add label blocks for them to fill in as we discuss them all. Future versions might have proper colour images pasted over the simple circles (printer access permitting) - though there's also something to be said for letting the kids colour them in themselves. And I'd really like to make (or copy) a version that shows the more interesting eccentric orbit shapes of the outer dwarf planets. You could also add asteroid groups, the Kuiper Belt, the Oort Cloud, whatever suits you.
The main thing I've learned by drawing my own version: It's not difficult to do a simple version, but doing it neatly is the real challenge. I used paint.NET's standard circle-drawing tool, and it's a pain.