Any 30x30x10mm aluminum-framed fan would work. I have the one in the link below in my Arrma Infraction 3s, and I have the 40mm version cooling the motor in my Radix6. These fans put out a ton of air and sound like a jet engine.
https://www.ebay.com/itm/383287950747?hash=item593dbdfd9b:g:rvsAAOSwB21evv2F&amdata=enc:AQAHAAAA4A0377ArPffbYFRIW/9cdJLz3HTgjSiacJ+0oMHogQ68plU9GvBxt3kxMLJjiIc11lI6YrlEc2DO8/0NI2joCZi7Mp6pXrNVATK0ubyKL0JBuhZMvBtXX7ktvtcsttZpw1jaw0a3AlKZdf9LbXHKbpSMrgJGO6qpOYBJWjnlmEPAS9EhU6t+rjgp1D2ozrhIZXyXGqbK2gOgcfg+WIWu0WYoJKp/WLW8jo6jjWGJBoWWpn+V88d17Lg/Oir3z3cH2AgZIY6sd5gcQhanpG6jTD19U5QnN7/QOcHZTrcbSDNk|tkp:BFBM2Iak0ONg
https://www.ebay.com/itm/383287950747?hash=item593dbdfd9b:g:rvsAAOSwB21evv2F&amdata=enc:AQAHAAAA4A0377ArPffbYFRIW/9cdJLz3HTgjSiacJ+0oMHogQ68plU9GvBxt3kxMLJjiIc11lI6YrlEc2DO8/0NI2joCZi7Mp6pXrNVATK0ubyKL0JBuhZMvBtXX7ktvtcsttZpw1jaw0a3AlKZdf9LbXHKbpSMrgJGO6qpOYBJWjnlmEPAS9EhU6t+rjgp1D2ozrhIZXyXGqbK2gOgcfg+WIWu0WYoJKp/WLW8jo6jjWGJBoWWpn+V88d17Lg/Oir3z3cH2AgZIY6sd5gcQhanpG6jTD19U5QnN7/QOcHZTrcbSDNk|tkp:BFBM2Iak0ONg