Asiana is a Star Alliance carrier, and should have access to Star Alliance partner award space, which you can generally search for on the websites of United or Air Canada. (freequentflyerbook.com)
(In a confusing twist, most airline programs use the word «saver» to indicate partner award space, while British Airways uses «peak.») (travelcodex.com)
Booked SWISS First One day back in November 2017 SWISS released partner award space in their First Class cabin. (milenomics.com)