Cooling Balm of the Warrior gives 1-2 defence 15% of the time. Bomberry Elixir gives 1 defence about 24% of the time. Silver Knight Negg gives 1-2 defence 100% of the time. But all of these are way, WAY more expensive than training at the school, as far as you're concerned.
The school is pretty much your only option if you really want a balanced pet. You're pretty far behind now (you'd have to train level a lot before you could train defence), but it's doable. It will be expensive and take a lot of time.
If you don't want to train defence, you can get percentage defence items or reflectors -- they don't rely on your boost. Ring of the Lost will block all dark, for example. Clawed Shield will reflect 60-80% of fire. All the breakable 50% reflectors will reflect 50% of an icon type thrown at you. Downsize! will block 50% of an attack. Basically, if you go on
IDB and look at defence items, avoid any that have actual icons shown, like
Leaf Shield with its 5 earth/5 water/3 phys. Go with ones that say they block all of an icon or reflect a certain percent, like the
Ring of the Lost or
Downsize!.