I got caught badly on this. Tried many many times on the last day to get through and make a booking for available TG flights, eventually got through - got put on hold for 50 minutes, but which time it was 12:10am and I was told US had exited *A - 10 minutes ago!
After getting out of the immensely frustrated mood that put me in, I researched flights on CX (I'm a member there - so logged in to check CX availability in F for several different itineraries).
I phoned US with these itineraries - NB, these are all available to ticket with miles on CX. None of them showed as available on the US operator's system. She said to call back later.
I would be curious to know if anyone has any success booking CX on US in the next few days... I have the miles, and I have three different trips to work on all with flexible dates. I'm just hoping this goes live soon (and that CX is not blocking the F seats).