Source?

That is an absurd statement. There are not 52 rules officials present during a major (that's the number of groups in the first two days).

I don't know how many rules officials work Tour events or at a major. It must be less than 18, though, because we often see a delay while a roaming official comes over from another hole. Seems like the final group at a major usually has a rules official with them, but that isn't true for every group, or else we would never see any delays in getting a ruling.

FWIW - Rules Schools are run jointly by the USGA and the PGA of America. They are four days long in which the rule book is covered from cover to cover. After three days of information, the fourth day consists of an examination. To become a USGA official you need to score at least 88 (out of 100), for the PGA Tour it goes up to a 92. To be ratified you must attend and achieve the minimum score once every four years.