What is the maximum allowed number of repeats in a Pokémon deck?
The official website does have the rules, and the maximum limit for any card is 4, unless the format restricts the card further.


  1.1 Constructed - In a Constructed event, players arrive at the tournament with a 60-card deck. The cards used to build the deck come from each player's personal collection. Decks may not contain more than 4 copies of a single card, as defined by the card's English title, with the standard exception for basic Energy cards. Some cards may have additional construction restrictions on them, which are treated as exceptions to the 4-copy rule. Matches are played for 6 Prize cards.