I managed to get hold of a really good case/cover.
Fits perfectly, has the correct cut outs in all the right places.
It came with a screen protector.
Even better, it has a magnet on the cover, so the tablet sleeps when the cover is closed, just like the original slide cover.
Unfortunately I can't post a link, but...
...Search for Fintie HP Slates 7 Extreme cover.