Stens Oregon & Rotary all market aftermarket blades and all of them have websites you type your details into to get a list of available blades.
You won't be able to byt them from the JD dealer as the franchise rules will not allow it but a small mower reair shop ( not a glass fronted retail shop ) should have accounts with the aftermarket supply chains.
Bad news is most blades now days are high lift due to the popularity of mulching.
If you can not find a low lift blade, remove a wedge about a 1/4 at the end from the flute at both ends of each blade.
Oregon make a Gater to fit your mower, however these tend to be higher lift but they are thicker wider & made from a totally different grade of steel so they might last a lot longer.