Finding positioning flights to a partner's international gateway is difficult, even on the west coast. I imagine having the AS single partner restriction makes it even more difficult. The reality is going to be that the only way you're going to get to JFK, PHL, CLT, MIA, or ORD is on AA. That will limit you to flying only AA for the international leg. So, you're either going to be extremely luck and find an all-AA award transiting an AA gateway, or you're going to have to purchase a positioning flight into a gateway where an AS partner award is available for that trip overseas.