Tim might have one in stock over at Best.
If not it looks like it uses a 25" belt. The model number is the FRX-25.0. If Tim doesn't have one The Needle Doctor has it for $15 or Garage-A-Records has it for $10.
Be sure to have your Dad pull the platter, clean the shaft and bearing with a lint free cloth and re-lube it with some synthetic motor oil (Mobil seems to be the choice by most).
While he's at it he could dampen the entire plastic plinth with copious amounts of rope caulk then take and dampen the aluminum platter too. He'll have to be little more exact with that one to make sure the platter is balanced after he gets it all installed. It will do wonders for the sound of the old Scott table.