Manufactured homes that are not attached to land are "personal property" they are not real estate but chattel mortgages. Consequently, they will not be foreclosed, but instead reposessed. These are usually taken back by the dealer that sold them. However, you can find them by finding the companies that sell them and locating their finance companies.
You can start here: http://www.homesight.org/edu/repossessed-modular-homes.html