A variety of houses for feral cats are available online at FeralVilla.com, Etsy.com and DrsFosterSmith.com. Many local pet supply stores sell outdoor cat shelters as well.
Feral Villa is a popular and well-reviewed source for wooden feral cat houses, but only one style is available as of 2015. Etsy offers a variety of styles from businesses around the world, while Drs. Foster and Smith sell a few types of fold-up fabric houses with heating options. Additionally, AlleyCat.org features a gallery of outdoor cat shelters from all over the web, with instructions on where to buy or how to make them.