funny you mention them I already have all of them, theres three actually =)
I was just looking for more decorations seeing as three aren't going to cut it for a 135g.
I was thinking the same thing, like using an old piece of wood as a base model and molding chicken wire around it then molding plaster around the chicken wire. After it had dried I could paint it any way I'd want and Voila! instant mangrove root entanglement. I just don't know how much that'd cost.
"I" wouldn't use plaster.
What I was going to do is get flexible tubing and fiberglass arond it and add bark texture with marine body filler. Then paint it with an epoxy paint tinted to a bark color.
In the paintingn above the roots look like tubes.