I would very strongly suggest hiring an electrician for this. Charge station pro instructions indicate using 3 AWG Copper, as long as you use THHN and install in conduit this should meet electrical code as well. Going to SE cable or trying to use Romex changes the temp rating on the wire, and you may have issues with larger wires fitting in terminals.
THHN is required to be run in conduit, if you want to save some money you can run the conduit for your electrician ahead of time. Your electrician will have no trouble getting #3 THHN from the wholesaler. Also, keep in mind that in many jurisdictions you should be permitting this type of work, as you are dealing with a large amount of current, and using the wrong size/type of wire can result in a fire.