In most cases you cannot book a BA codeshare flight on its own, only as part of a BA ticket with longhaul segment on BA or JV partner. They are predominantly offered on shorthaul routes not operated by BA from/to airports BA do serve longhaul, and on JV partner longhaul routes ex-LON.
QR does not offer many routes that would work as a BA codeshare, as BA serves many directly.
Look at the announcement BA made when the QR JB went live. That tells you the list of BA*QR codeshare routes (sorry I don't have a link to hand)