I am having problems booking any CO codeshares on NW (and conversely NW codeshares on CO) out of SAT. I have checked Expedia for the fare basis codes and the fares usually include connections at IAH/MEM/MSP/etc. However, I am unable to find a booking engine that successfully finds any of the codeshares. (They do exist because they are listed in the paper schedules every time.)

On the other hand, if I look for CO/NW codeshares out of AUS, the booking engines pull them up easily.

As an example, try AUS-SEA and you will get both CO flights and CO codeshare flights on NW. However, if you try SAT-SEA, only CO flights show up.

Do anyone have a solution??