We do carry convenience cords that would take the L14-30R (30-amp 120/240 volt) outlet down to (4) 5-20R (20-amp 120 volt) outlets. Check out the Conntek model #20611.
This is a 25-foot cord that costs $58.99. This cord branches from the L14-30R outlet and splits the two legs of 240 volts into 120 volts for each of the paired outlets resulting in (4) 5-30R outlets.