Here's my current post-rotation build. I've made changes to this list like 50 times to try different things out, but the general build is modeled of off Andrew Mahone's deck list (you can find it on Derium's Competitive Pokemon YouTube channel). I know you said you only have 3 Gardevoir at the moment so I recommend throwing in a Gallade for the fourth spot. Andrew was originally running a 1-1 line of Octillery and 2 Lillie. I removed those four cards and added in an Oranguru, an Acerola, and two Choice Bands. The Acerola and Choice Bands are flexible. If you're running Gallade, you might want to run Octillery for the Premonition/Abyssal Hand combo.
****** Pokémon Trading Card Game Deck List ******
##Pokémon - 17
* 1 Oranguru PR-SM SM13
* 2 Diancie BUS 94
* 4 Ralts BUS 91
* 3 Kirlia BUS 92
* 4 Gardevoir-GX BUS 140
* 3 Tapu Lele-GX GRI 137
##Trainer Cards - 30
* 1 Acerola BUS 142
* 2 Choice Band GRI 121
* 4 Professor Sycamore BKP 107
* 1 Professor's Letter BKT 146
* 4 Ultra Ball SUM 135
* 3 Float Stone BKT 137
* 2 Skyla BKT 148
* 3 Guzma BUS 115
* 1 Brigette BKT 161
* 4 N FAC 105
* 2 Field Blower GRI 125
* 3 Rare Candy SUM 129
##Energy - 13
* 4 Double Colorless Energy SUM 136
* 9 Fairy Energy 9
Total Cards - 60
****** Deck List Generated by the Pokémon TCG Online
www.pokemon.com/TCGO ******