Hello =) Can someone help me where exactly i can find the item at the cash shop? I feel so stupid...i searched for three times but couldn't find it at all xD

If it was there, I believe it would be in the Vanity section of Items.

https://subeta.net/ss.php/cashshop#/shop/Vanity

But it appears that it was retired and not added back to the shop for Black Friday.

its a retired vanity item, so it should be obtainable through the gift of fashions past.