I want to first say I know nothing about paladin shield preferences, but to say there aren't many mid quality shields I think is inaccurate.
There aint a lot in the way of mid-quality shields.
There are a lot of options for shields and a very clear progression path for tank shields with options at each step of progression. Of any slot, shields may be one of the few slots that prot warriors have a large number of choices.
1. [item]Shield of the Wayward Footman[/item] - BOE
2. [item]Platinum Shield of the Valorous[/item] - regular SL off first boss.
3. [item]Aegis of the Sunbird[/item] - regular Botanica
4. [item]Ogri'la Aegis[/item] - Ogri'la revered
5. [item]Crest of the Sha'tar[/item] - Shatar exalted
6. [item]Azure-Shield of Coldarra[/item] - 33 badges
7. [item]Gladiator's Shield Wall[/item] - 15k honor
8. [item]Shield of Impenetrable Darkness[/item] - Nightbane
9. [item]Aldori Legacy Defender[/item] - Gruul
10. [item]Merciless Gladiator's Shield Wall[/item] - 1630 arena points
11. [item]Bulwark of the Amani Empire[/item] - Jan'alai, dragonhawk
12. [item]Vengeful Gladiator's Shield Wall[/item] - 1875 arena points + 1850 rating
I don't see any gap in item progression there. There isn't a good "heroic" shield drop, but 2 faction shields, a badge shield and 2 pvp shields are options for any tank that puts in any effort.
I would think a prot war BP would be appropriate assuming the difficulty of the instance is on par with Karazan.
The beast is getting hungrier.