I somehow have the impression that your itinerary is not optimal.
You might want to list your complete itinerary, so we can see if there are optimisations possible. You could also post your travel plan on the Tripadvisor’s Switzerland forum; it is the best travel forum that I know for Switzerland travellers. They do have many locals giving great advice.
I can easily make a reservation for the 08:28 train from Chur on 26 October, there are many seats available.