To be perfectly honest, your best bet is what you mention in your first post: scratch build! Get some bamboo skewers for the base (set two in parallel for the length of walkway you want, plus a bit extra so it doesn't fall into the gap), and popsicle sticks for the treads. Use PVA or white glue to stick the treads onto the bamboo skewers and you're pretty much done. You can use a wire brush to slightly distress the treads (make them look like wood grain) if you want to get fancy. Use a stain or wash to add some colour (or go all the way and paint/drybrush). And you're done! Faster than ordering in special pieces from a vendor or three-d printing. And best of all, cheap!