I got my coolant lines from autoparts. They will sell you robber fuel lines which are better quality compare to stock. Bring your old line and they will match the size for you. Remember the lines they sell are straight and Mitsubishi is using lines that are bent! If you bent a straight line over 90 degrees you will reduce/close the diameter of the line. Don't bent them too much!

Also, make sure you buy smaller t-bolt clamps for those lines.