I have been searching, with no luck yet. I really loved the Speck folio case I had with my Mini 4, so I may attempt to drill small microphone holes in that case, since the iPad dimensions are exactly the same, and the volume buttons opening should accommodate the slightly larger volume buttons.
I have a brand new switcheasy canvas that I am hoping fits the new mini, my old mini 2 lives in one from when it was new so I'm really hoping it does as they are superb, best case for any iPad I've ever found.
Not sure if they make them anymore though.
Check out Twelve south bookbook case. I’ve got one on my mini 4 and plan on using it on my 5 when it gets here. They are going to have one out for the 5 shortly. Most likely will have pencil holder on the inside like my wife’s iPad Pro does.