I'm guessing the Kobo Aura HD had a short production run because it's very hard to find cases for them. But I did find a Navitech case on Amazon (in either grey or blue) for $4.99, plus $2.49 shipping (from England). The vendor who is selling them is North Laine Accessories US. I ordered a similar case for my Kobo Mini from them (it was selling for 99 cents and $2.49 shipping. I haven't gotten it in yet, but it has decent reviews on Amazon). If you want, I can report on its quality when it gets in. I don't know how someone can sell and ship a case for $3.48 from England (I also ordered one that's supposed to be a sleep cover for the Mini for $4.99 plus $2.49 shipping -- I didn't see the 99 cent one until later.) It's not easy to find covers for the Mini either, but next to the Aura HD it's child's play. (These are supposed to come in any time from tomorrow till next Thursday -- no tracking, so I can't tell exactly when.)
https://www.amazon.com/MiTAB-Leather...oding=UTF8&me=