the official Niantic support page for Evolution Items was updated, confirming that Deep Sea Scale and Deep Sea Tooth are the two new upcoming evolution items. The following text is now on the support page:
Select Pokémon require an Evolution item as well as Candy to evolve. There are seven different types of Evolution items (Dragon Scale, Deepsea Scale, Deepsea Tooth, King’s Rock, Metal Coat, Sun Stone, and Up-Grade) that can be used to evolve these Pokémon. You can collect Evolution items by visiting PokéStops.
DS Scale and Tooth are used to evolve Clamperl into a Gorebyss or a Huntail, depending which item is used, making this the Generation 3’s evolution line that requires a new item in order to advance.
As usual, these item will be available from PokéStop drops and there is no indication that the chance to obtain them will be increased on launch. It could be a while before you get both of them, given how large the evolution item pool is now.
In addition the two new items, the same page has confirmed that some Pokémon, like Feebas will have a walking requirement before they’re ready to evolve:
In addition to collecting Candy, select Pokémon, like Feebass, need to be walked as your buddy Pokémon before they are ready to be evolved.
At the moment, only Feebas has it’s buddy walking distance evolution requirement in the Game Master: