Are you sure they're available to partners and not special United-only awards? Can you select it on the United website, take a screenshot, and show us? If it's the YN (economy) or JN (business) fare bucket, it's United-only.
I have found partner-level award space between other cities (like HND-LAX, for instance), which is visible on other Star Alliance partners, but doesn't show up for Velocity. But it seems to be something to do with the Velocity website not recognising all city pairs for United yet. However I would definitely expect the flights to/from Australia (BNE-SFO, SYD/MEL-LAX/SFO, SYD-IAH and vice versa) to be bookable online if there is real partner space.