As James mentioned, they're probably the hardest set of chinscales to find (along with the curved silver mounted troops version as used on the 2-Hessian Cavalry Regiments, etcetera).
I have seen 2-sets sell on eBay (Germany & France) in the past 5-6+ years. They were both small size sets (for small size helmets) and in decent condition. I believe they sold in the $600-$700+ range back then.
Best wishes in your search.
Best Regards,
Alan