The OCA Exarchate of Mexico was built by a formerly independent catholic parish (near Mexico City airport). They got their original orders from clergy whose orders can be traced to the "National Catholic Church" (a breakaway group created by the Communists during the years of the religious persecution in Mexico, a kind of "Living Church" for Catholics). I must say, however, that this community had no actual relation with the Communist Church.
They were trying to join an Orthodox Church following the steps of other Mexican parishes in Texas and the Southern US who became part of the OCA. However, this was not possible in Mexico as the Antiochians had no interest in expanding their Church to non-Arabs. Joining the OCA predecesor was at that time not possible (as it wasn't recognized by the MP, the Soviet embassy and the pro-Communist government in Mexico would have opposed). However, in the 1970's, once the OCA was recognized by Moscow, the group was received as the Exarchate of Mexico.
I have personally tried to bring some independent churches to real Orthodoxy but many don't really have an intention to be canonical and do things correctly. they're happy to be independent and they don't want to follow the disciplines of the Church.