I found the following premiere dates on the Discovery ad sales page
Hard To Kill
Series Premiere August 7 | Tuesdays 10PM ET
Season 2 Returns September 24 | Monday at 11PM ET
New Season Premieres October 14 | Sunday at 7 pm ET
Alaska: The Last Frontier
Season 8 Returns October 14 | Sunday 9PM ET
The Last Alaskans
Season 4 Returns October 14 | Sunday 10PM ET
Above & Beyond: NASA's Journey
to Tomorrow Premieres October 21 | Sunday at 8PM ET
Canada's Worst Driver
Season 14 Premieres October 29 | Monday at 10PM ET
Other shows say "Coming soon," etc.
The fall 2018 grid is also available.