Variety columnist Bashirah Muttalib has a fascinating piece about the Herculean task the Frost/Nixon location manager had in trying to film key Orange County locations depicted in the film, which is set in the late 1970s.
The Richard Nixon Library and Birthplace in Yorba Linda opened its doors for location man Greg Alpert and the rest of director Ron Howard's crew. Access to La Casa Pacifica, the Western White House during Nixon's presidency and his former home with wife Pat, was more problematic. Writes Muttalib:
Securing that location was not an easy task as the home's current owners, who were friends and supporters of Nixon, were very private and protective of the property, having purchased it directly from the Nixons. They nonetheless allowed limited access for research purposes only, flatly denying all filming even for reference pictures.
Alpert's team searched the coast from San Diego County to Santa Barbara County for a suitable La Casa Pacifica stand-in before settling on–and getting the blessing of–a Palos Verdes Estates church that used to be a residence. But Howard apparently still wanted some La Casa Pacifica elements the church lacked. So Alpert returned to San Clemente, did the hard sell on La Casa Pacifica's owners and was finally granted two days of filming. Again, Muttalib writes:
According to Alpert, stars Frank Langella [Richard Nixon] and Michael Sheen [David Frost] expressed deep satisfaction at working where the events depicted actually took place.
The televised interviews in '77 were actually filmed at the Monarch Bay home of a Nixon crony, but the look of it had changed so much in the ensuing years that filmmakers had to find a double for that one as well, in Thousand Oaks. Alpert and his team were able to snap photos of the Monarch Bay home's interiors and exteriors to help with set design, however.