A Old Trainers, New Megas series of art would be fire from Tom. Some of these might be shared to doubles if he wants to

Also worth noting he already done Emmett and Ingo with their megas

Lt. Surge - Mega Raichu X
Red - Mega Raichu Y
Erika - Mega Victreebel (there’s also James , hence the fanart)
Misty - Mega Starmie
Lance - Mega Dragonite
Jasmine - Mega Skarmory (Winona would also work)
Larry - Mega Staraptor
Volo - Mega Garchomp Z
Candice - Mega Froslass
Clay - Mega Excadrill
Roxie - Mega Scolipede (alternatively Klara, since Galarian Slowbro can’t mega evolve)
Grimsley - Mega Scrafty
Elesa - Mega Eelektross
Shauntal - Mega Chandelure
Malva - Mega Pyroar
Olympia - Mega Meowstic
Grant - Mega Barbaracle
Drasna - Mega Dragalge
Hala - Mega Crabominable
Guzma - Mega Golisopod
Bea - Mega Falinks
Arven - Mega Scovillain
Geeta - Mega Glimmora
Hassel - Mega Baxcalibur