I found out that you might get it from getting the national dex done (besides event pokes) and you get an apricorn from professer oak and you give that apricorn to kurt and he makes the gs ball. I'm testing it now
You'll be able to get it by a nintendo special event
From a nintendo event which will happen very shortly from kurt I can't [email protected]!!
You can't get it on your own you can only get the GS ball from Kurt by a nintendo special event.
You get the gs ball from mr.pokemon by giving a flying pikachu