Try using only one lead of the signal injector versus one lead to ground and the other lead on the line that is shorted.
It might radiate enough to chase the line down.
Since you should know which outlets and devices do not work with the breaker popped then you may need to pull each outlet out of the wall for inspection and while doing so you may find a junction box where a wire has worked loose from a wire nut.
Myron & Deborah
08 HR Endeavor 40 SKQ
2016 Ford F150 Limited V6 with Ready Brake
Aluminator tow bar, Demco base plate