South Park (Lost Mexican Spanish Dub of Animated Series; 1998-1999)
In 1998, South Park began airing in Spanish on a local Mexican channel. The company that dubbed it was Audiomaster 3000, known for dubbing many foreign shows into Latin American Spanish. This dub covered the first two seasons of the series.
This dub was not in very high favor with Latin American audiences, mainly because of the fact that a lot of the profanity was censored and replaced with Mexican slang terms. The poor ratings and reception lead to the dubbing being discontinued.
Around the same time, another Latin American Spanish dub (produced in Miami, Florida) had began airing on Locomotion, dubbed by BVI Communications for season 1 and part of season 2, and Globecast Hero Productions for the remainder of its season 2. It found greater success due to the fact that it was less softened in the profanity department. This dub would shift through various ADR studios afterwards, and channel-hopped from Locomotion to MTV Latinoamerica in its eighth season.
Bigger, Longer & Uncut
The film of the series, South Park: Bigger, Longer & Uncut, also has two Mexican dubs. The first dub was produced by Warner Bros. in 1999. This dub was censored, with the songs subtitled. An uncensored dub was produced by Paramount in 2007 with dubbed music.
Note that Paramount distributes the film in the United States, while Latin American rights are held by Warner Bros.
However, neither dub of the movie is considered lost, as the American Blu-Ray uses Paramount's dub, and the Warner Bros. dub is broadcast on cable television (sometimes, ironically enough, on the Paramount Channel) and is available on Netflix.
Reason For Dub Loss
This dub is likely completely lost as not many people liked it, which would mean that less people would have recorded it onto personal tapes, leading to it fading into obscurity.
Audiomaster 3000, the dubbing studio responsible for the Mexican dub, went out of business in 2003. The company's assets were acquired by Candiani Dubbing Studios, and the Audiomaster name was retired until 2016.
Another reason is because of the aforementioned BVI dub's popularity, between its initial dub of seasons 1-2 and the more recent 2011 redub done to keep voice cast consistency. On the Televisa DVD releases, the 2011 dub by BVI is used for the first two seasons, except in at least two exceptions; "Mr. Hankey the Christmas Poo" used the original 1998 dub by BVI due to strong criticisms of the redub's lyrical adaptations.
In the second case with "Chickenpox", a more peculiar situation occurred, and is noted below.
Season 1 in its entirety has been lost, and may have possibly been wiped by the network. However, some small parts of Season 2 have been easier to find, as MTV Latinoamerica aired this version once later on in its broadcasting of the show (due to Locomotion not being able to locate the BVI/Globecast version to pass on to the network).
According to the Spanish Dubbing wiki, the first season of the Mexican dub was broadcast in Peru as late as 2011. However, there are no records of that audio at all.
Two full episodes have been unearthed on Televisa's DVD releases. The Season 2 boxset uses the Audiomaster vocal track for "Chickenpox", while the Mexican dub of "Merry Christmas Charlie Manson" is available on the Navidad en South Park ("Christmas in South Park") compilation.
The theme song for season 2 can also be found, however, the original season 1 version is still missing. There is a slight difference between both openings, as Carlos Inigo's vocals for Stan were redubbed with Eduardo Garza's after the role had been recast.
Fragments of found season 2 episodes include "Gnomes", "Cartman's Mom is Still a Dirty Slut", "Clubhouses", and "Chef's Chocolate Salty Balls", all available on DailyMotion.