The supply of LP box sets put out by Reader's Digest in the 1960s and '70s seems endless. Most of these can be bought for peanuts at garage sales and thrift stores, so you can safely ignore the mostly ridiculous prices being demanded online.
These recordings may be cheap to obtain, but don't make the mistake of thinking they are substandard in quality. For the most part the Reader's Digest boxes are excellent technically. Musically most of them tend to stick to easy listening and background music, with occasional forays into light classical and jazz. Many of the tracks were repackaged, often several times, in different box sets. This continued into the CD era.
Like many of the sets South of the Border (1968) mines the vaults of RCA Victor. The majority of the tracks on the four LPs were recorded by RCA in Mexico and their release by Reader's Digest was their first appearance in the U.S., Canada and the U.K.
Among the Mexico-recorded tunes is Cachita by Tonio Rivera and His Orchestra. This name does not seem to exist outside the Reader's Digest releases and is likely a moniker assigned to a studio group.
Since the music on Reader's Digest box sets has been endlessly repackaged, both on LP and CD, it's difficult to tell what, if anything, is available from South of the Border. Best bet, as I said at the start, is to watch the garage sales and thrift stores for the vinyl.
One of the most common Reader's Digest boxes is Mood Music for Listening and Relaxation (1963). This must have been a pretty big seller, judging from the number of copies still around. Here's a sample track, which was likely recorded in England.