The wand is in the shop, but it's unclear wether the Frost wand is meant to be shown in the shop or if it is meant to be hidden in the shop.
You are able to buy the wand, but if you want to do so, you'll need 250K spirits and follow this step below:
Click every empty slot in the shop (every slot without something in it, meaning a slot without armour or a book)
Eventually you'll click the slot which contains the Frostspark wand and you will automatically buy it for 250K spirits when you click it.
I hope that I helped you.