"We are still casting for the fourth episode," she said.
RDF is accepting new applications, too.
The reality show, which is scheduled to air this summer, takes a mother from one family, switches her with a mother from another family for 10 days and films them.
"During the first five days, the Moms try to fit into the routine and adopt the lifestyle of their new family, giving all a chance to become familiar with each other," a description of the show says. "For the second five days, the new Moms make any changes they see fit and run the home in a way that suits them."
The families talk about the experience afterwards.
The show is based on the British show "Wife Swap," also produced by RDF.
The Guardian newspaper of London recently described "Wife Swap" as a "runaway reality hit." However, one episode - in which a white woman opposed to "mixed marriages" was paired with a black man who repeatedly insulted her - was "some of the most jaw-droppingly ghastly television ever broadcast," the Guardian wrote.
Dervan said the American version will be toned down and aimed at a family audience.
The Associated Press reported last week that a Turkish couple on the Austrian version, "Family Swap," faced ethnic epithets during one episode, sparking a national debate on racism.
Dervan said RDF is not involved with the Austrian version.
For the American version, Dervan said, RDF is looking for families with "unique relationships or strong opinions."
Families must have two parents and have children older than 2.
The application form, which is available at the show's Web site, asks how long parents have been married, what their schedules are, how much money they spend on entertainment and who handles which responsibilities, such as shopping, cleaning, cooking, social planning and children's homework.
Dervan said RDF is focusing its contestant search on communities east of the Mississippi River. Hagerstown was targeted because a few people expressed interest by e-mail before the show was publicized in the media, she said.
A search of newspaper clips on the Internet shows that RDF also has recruited in Cumberland, Md.; Salisbury, Md.; Natchez, Miss.; Hornell, N.Y.; Opelousas, La.; and Helena, Ark.
Dervan said hundreds of families have submitted applications.
She would not disclose the hometowns of the contestants selected so far.