Here are the best places to EV train in Shinnoh.
*VS Seeker*
HP:
Route 209 - Cowgirl (?) - L14, 15, 15, 15, and 16 Bippa (5 HP)
Route 210 - Bird Tamer (lower level) - L38 and 42 Noctowl (4 HP)
Route 212 - Fisherman (lower one) - L17, 17, and 18 Barboach, L20 Karanakushi (4 HP)
Route 213 - Male Tuber (pacing) - L52, 53, and 51 Toritoidon (6 HP)
Route 219 – Female Tuber – L29 and 29 Marill (4 HP)*
*Not recommended because she’s on a very small island with confined movement.
Attack:
Route 203 - Lass (upper area) - L38 Mukkuhawk, L38 Biidaru (5 Attack)
Route 214 - Gambler (? guy flipping coin) - L36 Goldeen, L37 and 38 Seaking (5 Attack)
Route 218 - Fisherman (bottom one) - L53 and 53 Gyarados (4 Attack)
Route 222 – Fisherman (leftmost) – L53 and 53 Gyarados (4 Attack)
Route 225 – Cooltrainer (standing still) – L53 Pinsir and L53 Mightyena (4 Attack)
Defense:
Route 210 (tall grass section) - Ninja Boy (middle) - L23, 23, and 26 Geodude (3 Defense)
Route 212 - Collector - L17, 18, and 19 Geodude (3 Defense)
Route 221 – Collector – L51, 52, and 53 Hippopotasu (3 Defense)
Special Attack:
Route 212 (rainy section) - Male Pokemon Ranger (northwest end) - L21 and 21 Pottaishi (4 Sp. Attack)
Route 212 (rainy section) - Scientist (?) - L53 and 53 Alakazam (6 Sp. Attack)
Route 214 - Male Psychic (spinning, pacing) - L38 Haunter, L42 Kadabra (4 Sp. Attack)
Route 214 - Collector (right path) - L20, 22, and 24 Roselia (6 Sp. Attack)
Special Defense:
Route 210 (foggy section) - Ninja Boy (upper level) - L27 Dustox (3 Sp. Defense)
Route 230 – Female Swimmer (bottom of pair) – 50 Tamanta, L52 Mantine (3 Sp. Defense)*
Route 230 – Female Swimmer (pacing, spinning, in top row of rocks) – L50 Seel, L54 Dewgong (3 Sp. Defense)*
*Not recommended because you'll have to Surf to recharge the VS Seeker in these places.
Speed:
Route 205 (water bridge) - Fisherman (second from right) - L10, 10, 10, 10, 10, and 10 Magikarp (6 Speed)
Cycling Road - Male Triathlete (third male from top) - L37 and 39 Mukkubird (4 Speed)
*Wild Pokemon*
Attack:
Twinleaf Town - Small Pond(Super Rod) - Gyrados(2), Seaking(2)
Defense:
Stark Mountain - Weezing(2), Macargo(2), Gravler(2), Onix(1)
Special Attack:
Old Chateau - Anywhere - Gastly(1)
Acity Lakefront - Surf - Psyduck(1) and Golduck(2)
Special Defense:
Route 223 - Surf - Tentacool(1), Tentacruel(2), Mantyke(1)
Speed:
Turnback Cave - Golbat(2)
Any body of water - (Old Rod) Magicarp(1)
Route 209 - Starly(1) and Staravia(2)
(mods edit if u want :D)