Yes, you can buy replacement Tekonsha wiring harnesses. Plenty on ebay.
I would suggest yours has been wired using a harness as they come with a harness in the box. If so, trace it back to where it is joined and snip the four wires. Fold each wire back on itself about 1cm and tape with insulation tape. Leave the wires in the car under the dash. Maybe cable tie them up. Job done.
KB