Before paying for anymore alignments, you really need to confirm the condition of all of the suspension components. If you put the front end on jack stands
and remove the wheels you can visually inspect the inner A-arm bushings. Are they cracked or separated? Beyond that, you can grab the rotor and hub assembly
at 3 and 9 o'clock and push in and out towards the engine and back to you. It
helps if someone else can look for movement from the inside of the control arms.
Beside that, listen for clunking and feel for looseness. Up and down play in the whole strut housing usually indicates wear in the upper bearing mount. Grab the end links of the stabilizer bar and check for play. Same thing for the tie rod ends. Move the rotor assembly to check for ball joint looseness.
Are the upper strut mount nuts inside the engine compartment tight? After ruling out all of these items, the rapid outer edge tire wear really sounds like too much tow-in. Did you get a read out from the alignment shop? Did they perform a four wheel alignment along the thrust angle?