You can try these :
http://www.agrisupply.com/kubota-mower-blade/p/86934/
I have ordered blades for here (not gator) and the quality was excellent.
And
Oregon 396-612 Grasshopper Gator Mulcher 3-in-1 Replacement Lawn Mower Blade 21-Inch
https://www.amazon.com/dp/B004LXIPG8/ref=cm_sw_r_cp_api_NI82ybK5D5G65
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