First, Gallade is not a Wall. He's a tank. He can take a few hits, but he can't switch in on a Poke and stop it from doing a thing. There's a HUGE difference.
Also, JESUS CHRIST there are other items besides Choice items. Speaking of which, Calm Mind and Recover on a Choice Specs Alakazam? Come on.
First, you need a lead. You could try Porygon-Z.
[email protected] Choice Scarf (I know it's a Choice item, but a Scarf completely changes how Z works.)
Modest
252 SAtk/ 252 Spd/ 6 HP
-Tri-Attack
-Thunderbolt
-Ice Beam
-Dark Pulse