It is authentic (it is Zags store after all) but it is never going to look like exactly what the players are wearing. This season they only have white Zags limited (vintage, check the shorts also) edition available and youth navy in new design. There is also the old design from last season. You may need to wait until another season for the new navy or white design with Gonzaga on it rather than Zags, but there is no guarantee it will have no. 1 on it.
P.S. I expect them to wear the new Zags version for the game against Baylor only.
Probably the only Gonzaga fan in Ireland!