yea, there arent any. I did find some with only one weakness: Pure Normal types (weak to Ghost), pure Ice types (weak to itself), Water Absorb Lapras (quad weak to Ice), Psychic/Dark types (weak to Psychic)
There are also a couple that don't exist in cart but have 1 weakness: Grass/Rock types with Lightning Rod/Motor Drive/Volt Absorb (weak to Normal) and Ice/Ground types with Lightning Rod/etc (weak to Poison).