"Your (leveling) guide mentions a caster sword is good for tanking. Is there an instance that that drops or is it an AH buy?" - Gemosi
It's the mantra of the Paladin Tank: "Warrior Gear, Spell Damage Sword".
While some truly gifted pioneers made Paladin Tanking work pre Burning Crusade, it didn't really come into its own until Patch 2.0 (last patch before Burning Crusade released). More so, one could argue that Paladin Tanking hasn't really been accepted until this last patch.
Sometimes, one will extrapolate that they way things work from 60-70 must be the way they work leveling up as well. This isn't always the case.
The lowest level equipable Spell Damage weapon that a Paladin can use is the Arbiter's Blade. It requires level 48 but drops from Warder Stirgess in the Vault in Black Rock Depths. It is highly unlikely a toon sees the inside of BRD before at least level 50.
The next option is the Energetic Rod. This drops off the last boss in Dire Maul: East. In Dire Maul: North, you'll find the Mind Carver off of Prince Tortheldrin. Ask a Warlock or Paladin wanting their Epic Mount quest done how easy it is to get DM groups these days.
Then we come to the Mastersmith's Hammer. This drops off a Rare in BlackRock Spire. That's a 10 man Level 60 Raid.
The last drop is the Hammer of Divine Might. This drops off of Kormok, a boss who was spawned in Scholomance by someone working on their Dungeon 2 quest line. I'm going to go out on a limb here and say that he doesn't get spawned much anymore.
There is also the epic Bind on Equip craftable sword, Sageblade. The big issue with Sageblade beside the expensive mats is that it requires level 59 to equip. By that point, you are across the portal and working on Questable Tankadin Weapons.
So I've revised that part of the guide. Find a fast 1 hander, and judge Crusader on your mob. Consecrate and Seal of Righteousness procs will be the building blocks of your threat, but don't underestimate how much threat your normal "white" damage is doing.
The other thing you can do is look for are greens and blues with what are called Random Enchants. These are things like "Of the Bear" or "Of the Eagle". One of the Random Enchants is "Of the Crusade" which is spell damage, and defense. I'm not sure what level items can get that one though. There is also "Of the Knight" which has spell damage and defense.