Gladius Legis
Legend
I am not sure why you "don't hear about two weapon fighting paladins" but my impression is that the off hand is often needed holding/focusing on your holy symbol and/or healing in combat. If you put the holy symbol on your shield, you could at least have a benefit to AC that way.
You don't need to hold a holy symbol. Wear it around your neck if you don't have a shield.
You need a free hand to perform somatic components, but if you need to do that, just stow away your off-hand weapon that round and cast, since it's not like you're attacking with your off-hand that round anyway. Then draw your off-hand weapon again next round.