Essentially there aren't very many of them - only a very small percentage of seats on each flight will be made available as reward seats (even if it's wide open for cash bookings).
And they become available as and when - ie not necessarily on the day the flight opens for general booking at T-330.
You can check availability by selecting "spend miles" instead of "spend money" in the booking engine. Just don't be surprised if there's no availability on the dates or flights you want. Your chances will improve if you can be flexible with your dates, and bear in mind if nothing's available on day 1 it may become available during the year, you just have to keep checking.
However if there IS availability get straight on the phone and book - the seats won't last long, especially in UC.
Good luck!
And they become available as and when - ie not necessarily on the day the flight opens for general booking at T-330.
You can check availability by selecting "spend miles" instead of "spend money" in the booking engine. Just don't be surprised if there's no availability on the dates or flights you want. Your chances will improve if you can be flexible with your dates, and bear in mind if nothing's available on day 1 it may become available during the year, you just have to keep checking.
However if there IS availability get straight on the phone and book - the seats won't last long, especially in UC.
Good luck!