Firtharos

Have you already done the pinkan island quest? If not, then there is still a npc that asks for your pokeballs when you go to pinkan forest. When you go back, he gives you your items back. This actually retrieved my pokeballs and items i had to turn in at the start of the heatran quest. How this works is that I think there is only one 'list of confiscated items', where everytime your items get confiscated, That exact list gets updated. So it doesnt matter if its for the heatran or the gengar quest. You might try that if you haven't already done the Pinkan questline

Just saw this in a developer preview, so there are more megastones on their way :)