I found small carry bag for Pinephone Keyboard (Pinephone wiith Pinephone Keyboard option):
Fjällräven High Coast Pocket F23226 (code is important to get carry stripe, there is another without it)

It has two pockets, bigger pocket is like designed for Pinephone Keyboard, smaller pocket is like designed for charging cable and small charger (like Deltaco DBS15Q) or surprisingly another Leste devices (N900 or Droid4) fits in.

It has disconnectable long carry stripe or you can use with your belt to carry on.

Bad point is that it is very expensive compared to size.