You have to make one. 21 amps, you need a 10 gauge conductor. 240 volts? 3 pole, 4 wire SJOW service cord with the right receptacle (NEMA 6-50 R) on one end, pigtails on the other.
With the SJOW wire, you have 4 conductors, black, red, white and green. Black and red are the legs, white is...