for the shield i would suggest http://www.wowhead.com/?item=45450 you have 2 way of getting it
a- go kill hodir 25 and hope
b- the best way, check the auction house and hope too
10 man Anub and 25 man Beasts drop a Shield.
10 man Anub and Onyxia drop decent tank weapons.
Twin Valkyr, 25 man Anub and Onyxia drop rings.
Replace 1 of your trinkets with the armor trinket from badges, it will beat them on any encounter that doesn't have incredibly huge magical spikes.
Now some things that bother me:
You need Glyph of Divine Plea -> Drop Judgement or Rigteous Defense , because both of them are rather bad.
Enchant 22 Stamina on your boots, because the speed enchant doesn't stack with pursuit of justice.
There is no def cap it's a minimum to be "immune" to crits -> gem Stamina+Def, because 10 def beats 3 stamina easily.
2% crit is pretty weak, so you'd better spend 2 of the points you put into conviction into Vindication (~15% less damage taken).