Hi Jiao,
You can also buy the bundle using PayPal or a debit card here on Itch.
about Unity, I'm already publishing Minifantasy packs in the Unity asset store, however, due to the large number of packs in the collection, and the particular requirements of Unity to be able to publish assets in their store, packs aren't being published there as quickly as I would like.
There are 7 packs currently available in Unity (and several more in the process of being published), out of the 35 available in Itch. But it will take a while yet to have all the packs in the collection also available in Unity.