I also plan DL first and it your situation when the return has no availability
I check partners like CO or NW.

Best to plan out (on paper as far back to 331 days as you can)
first, second, and even 3rd choices THEN BOOK right then and there.
For $50 you can always change later when availability is better,
OR, should you need to cancel, the miles go on back to your account.

On the same subject, (especially flying international) ALWAYS get
travel insurance to cover medical and unforeseen events/delays as
there is often NO compensation for delays/cancels on Non-Rev
(Award) tickets- (unless your high up the PE line).