I wanted to tell that I have talked to him and got all the details.
Just say" I talked to him and got all the details"
When you say "I could talk him and get all the details" it means you haven't talked to him and concequently haven't got any details" and maybe you are sorry in a way.
The subjunctive deals with potential state, condition, or situation, so if someone says they could do something, there seems a clear suggestion that the state, etc., must exist before they will do it.