Unless you want something big, and RC,
The only tugs I can recall seeing are the
Revell Smit Frankrijk, Revell Harbour Tug Boat 5207'
A Heller Smit Rotterdam, and the Lindberg Harbor Tug.
The Lindberg is a small 1/82nd scale 1950s style tug boat.
Everything else is pretty big and made for pond running.Harbor Models
has a good selection. If this scale interests you, browse their website, and see what you can find available locally.http://www.harbormodels.com/Harbormain/Templates/index.htm