That’s not really something you can estimate since we have no idea on the size of the print run. The pull rate is supposed to be one every 2-3 boxes (I think I read somewhere that it was 1:72 packs), then take into account that there are multiple gold stars in each set making the chance on getting the one you want slim even if you do pull one … so they’re rare, for a set card - as for numbers in circulation, who knows.
That said entei, raikou and suicune are not rare due to this: www.elitefourum.com/t/mystery-of-the-entei-suicune-and-raikou-goldstars/13863/1