They could even make a pokemon that looks like a shield
They already did. And its counter part has very high attack although its not a sword.
Are you talking about Shieldon & Bastiodon, they look more like they were based off dinosaurs then shields to me, but I guess they can make another pokemon that more closely resembles a shield.
Actually, the Shieldon and Craniados lines are based on an old legend of the spear that pierces any shield and the shield that blocks any attack.
A merchant brought both weapons to the emperor claiming they could do such a thing, but the emperor pointed out the flaw in his logic by saying if that spear could pierce that shield, the shield can't block any attack and vise versa.