Hi Matt. Ive seen a method somewhere, where the modeller, used small branches as the base ... in a straight row. No need to have the spaces the same as hedges grew sort of wild. Then they used a wire scrubbing pad, pulled out and shaped to bulk up the hedge and give it form. Then the usual flocking and herbs were glued to give hedge shape.
When painted this looked quite effective. The advantages of this method is you can build the hedge to the dimensions that suit your dio. The only "buyable" hedges that I know of, are games workshop, and these wouldnt come close to the previous type. Just an option for you if you´re interested!