I made a dark link sword for my DL cosplay, I made it entirely out of fiberglass, bondo, and resin, with a couple of wooden dowels for support. This is how it looks:
I've never seen one online for sale, at least not plastic, there's a cheapo wooden one online that I would suggest avoiding like the plague. It's a complete ripoff.
If you don't want a steel one, but you still want a quality sword that wont break and looks like a legitimate replica, you'll either have to craft one yourself or commission someone to make it.