There is nothing in the fare rules of an xASnn ticket requiring that the operating carrier of the first international flight issue the ticket. Further the oneworld website says to contact any member carrier about ticketing.

The rules also state that AA and IB can issue Circle Asia tickets, even though they do not operate any flights within the allowed travel region.

The Oneworld Explorer online booking tool sends the itinerary to the marketing carrier of the first flight, not because of a rule, but because of a technical limitation.

So, please, provide a quote.
Thank you.