This wonderful addon adds shields to the game.
Mod replace trident on shield.

As it is the Trident which is replaced by a shield you might need to enable Experimental Features for a world in the world settings in order to be able to find it in-game. The easiest way to obtain the shield item is to search for it in the Creative Inventory.

NOTE: You also have BlockLauncher for install mod and skin for minecraft pe.

DISCLAIMER: This is an unofficial application for Minecraft Pocket Edition.
This application is not affiliated in any way with Mojang AB. The Minecraft Name, the Minecraft Brand and the Minecraft Assets are all property of Mojang AB or their respectful owner.
All rights reserved. In accordance with http://account.mojang.com/documents/brand_guidelines