I know the more attainable and realistic guys are Russell (maybe), Randle and Vucevic.
However, once free agency starts at 6pm on the 30th, the first guy I call if I am Ainge is Kemba Walker.
He may or may not stay in Charlotte but that team is going nowhere and are saddled with bad contracts.
I know he'll get tons of interest from other teams with cap space, but just the thought of seeing him replace Kyrie next year would be great! I know it's unlikely, but that would be my first target.
Aim high and work your way down.