Mark, unless you concentrate your efforts in the tackle shops area, you're gonna be hard pressed to find an ostrich duster. Most now are made of turkey feathers. The ostrich plumes sold in the craft stores contain fine barbules; the kind most likely used on fresh patterns and very small salt stuff. No real length to the material at all. Perhaps trying a industrial cleaning supply company will help.
This admission may shock the venerable President of the Gearheads, but I must admit to it: I do not have a resource for any and all things