One alternative is to use pheasant tails. Just about any long pheasant tail will work. I like Amherst (especially dyed different colors), Golden (see picture below) and Silver or Ringneck will all work. The key to making it work though, is having a "supporting underhackle" of some sort. A simple wrap or two of dyed mallard flank, long schlappen, even blue eared, or ringneck under the pheasant tail will support the long fibers.
Once the body is wrapped leave ample room for the supporting hackle. On the fly pictured I just trimmed olive marabou fibers off of the rachis and tied it in two bunches, rolling it over the hook shank and then using a soft loop to anchor it. This is exactly what you need to do with the pheasant tail fibers. I look for pheasant tails that have fibers that will not marry well. Usually these are the low grade tails that I can't use for full dress salmon flies. I trim 6-10 fibers from the rachis and place the bunch over the shank of the hook, I take a soft loop to anchor them, and press on the bunch of fibers with my thumb to help spread them around the shank even further. You may need to add multiple bunches to get the look you want. Then just trim the ends of the fibers short, add a wing and you've got a pretty slick spey fly. Give it a try, I think you'll like it!