Does anyone know where I can get a new wheel? I need the left rear power wheel and probably all the attachments.

Check eBay, they are listed frequently. Same as sears. The Central Park is made by AYP, should be on label under the rear seat.

What do you do if there is NO label under the seat? I can't find the model or serial #.

I assume you have a central park mower. They were made by AYP. The model number is composed of the horsepower and width of cut. My mower has a Briggs and Straton 12.5 horsepower engine and is a 42 inch wide cut deck. A letter follows, but that just gives the year, which isn't as important. Thus, my model number is CP 12542. CP=Central Park, 125=12.5 HP 42= 42" cut. The horsepower label is on the engine. If yours is a 17.5 HP 38 " cut, your model would be CP 17538. There are online mower parts places that you can use to get parts diagrams to order part numbers that you need. Fortunately, one of them is local for me too, so I can go in person to order parts.