I have the answer for regirock but not for regice or registeel:
This set of regirock seems legit (not great but not horrible):
Clear Body, then Aerilate
HP80 Atk 130 Def 220 SpA 60 SpD120 Spe70
EVs: 252Att 252Vit 4SpeDef
Jolly
Rock Polish
Explosion
Stone Edge
Earthquake/Return
Thanks to...