Where can I find knives for a Frontier DM5070 disc mower??

I bought a new Frontier DM5070 disc mower, its a 9ft something cutting width, and after talking to JD parts come to the sad realization that something as simple as cutting knives for that model are hard to come by and expensive!  Almost $17 dollars a piece going through Deere.  I see other disc mower knives for like 2 or $3 bucks a piece for other models.  Can someone please give me some insight on where I can get knives for this model mower cheaper?  What knives could interchange with this mower?  I hear Kuhn makes the Frontier disc mower line, would knives on their similar model disc mower interchange?

 

Any positive help would be appreciated.

Where can I find knives for a Frontier DM5070 disc mower??