Thanks to Dan McDonald (kebe.com) we now have a US mirror for our downloads and core package repositories.
To add this mirror to your configured omnios publisher, use the -m parameter to pkg set-publisher as shown below, replacing r151048 with the version that you are running.
# pkg set-publisher -r -m https://us-west.mirror.omnios.org/r151048/core omnios
The mirror can be used for all currently supported releases and bloody.