I know I might have given enough suggestions already, but I feel like I should say just two more. These could be either Gym leaders or part of the Elite Four.
Pokemon Type: Electric
Gym Leader's Name: Doesn't matter, but I was thinking Ava or Evelyn
Appearance: Female, Golden yellow hair with green eyes
Example Pokemon: Magneton, Raichu, Manectric, Electabuzz, Flaafy
(There's never been a female electric Gym leader or Elite Four member.)
Pokemon Type: Ice
Gym Leader's Name: Doesn't matter, I can't really think of a good name for him
Appearance: Male, Royal blue hair with silver or light blue eyes
Example Pokemon: Snorunt, Jynx, Dewgong, Mamoswine, Walrein, Weavile