Call Sunbeam. Phone number in the manual. Not posting phone number here because so many spam messages here have bogus phone numbers that are fradulents.
Unfortunately it doesn't appear that these motors are available. About the only thing I can recommend is to Google "appliance repair" and all of the local appliance repair services in your area should pop up. These guys can either find a match for these rotisseries or figure out where the motors can be rebuilt.