I finally found a 4020 blower fan. He should just upgrade to a 5015 anyway.
1 Pcs DC Blower Fan 24V 4020 2 Pin Black 40x20mm Brushless DC Cooling Blower Fan https://www.amazon.com/dp/B00KFY1L18/ref=cm_sw_r_cp_api_glt_fabc_9VS439E5E5E4BV3GX8SB
Isn’t that just a 5015? They are all over Amazon...
edit:
here
1 Pcs DC Blower Fan 24V 4020 2 Pin Black 40x20mm Brushless DC Cooling Blower Fan https://www.amazon.com/dp/B00KFY1L18/ref=cm_sw_r_cp_api_glt_fabc_9VS439E5E5E4BV3GX8SB