Contact Old Glory and see if they'll part them out for you. It's worth a try. I feel like they have done that for people, I've also heard they don't separate individual figures from packs. The reason I'd ask is because the shields might be on a separate mold.
Go through this site:
http://oldglory25s.comOld Glory is odd in that they have their own site, and a third party site that submits orders back to Old Glory proper... at least that's how I understand it.
If you can't, to get that number I'd do something dastardly... get one shield of whatever type you want, sculpt your own, add detail to one of the shields you already have to diversify it, whatever... then buy some 'Insta Mold' and greenstuff/sculpting putty and press mold them.
http://www.coolminiornot.com/shop/instant-mold.html