Estes and Quest have plastic fin cans in a few sizes including 24mm and near 29mm. Estes has the fincan from the Eliminator that is fits the BT-56, which is a tad larger than a 29mm tube, but could be used; Quest has the can from the Brighthawk that is that approximate size as well (although the old can from the very similar Falcon was nicer). Nevertheless, Estes and Quest both have a few plastic fin cans in that range
Performance Rocketry sells two styles of their fiberglass fincans for 29mm tubes: a three finned Nike style, and a four finned Apache style.
Hope this helps!
-Eric-