Evolution items are one of the few additions in Pokémon GO Gen 2 patch. These unique items, similar to the previous Pokémon games, enable a particular Pokémon specie to reach its final evolution form. As known earlier, Evolution Items can only be found via spinning the PokeStops. However, it has a very low drop rate.
According to Mic, one fan reportedly posted a new case to get a particular evolution item. As posted on the Silph Road, a user named Marvel227 claims to receive a Dragon Scale after walking approximately about 1 Km with Seadra. This Pokémon is known to evolve using a Dragon Scale. It was then suggested that the evolution item drops might depend with the trainer chooses as a buddy Pokémon.
The said redditor noticed this case due to the earlier post made by user Oxone_PkMnTrnr discussing a similar case. Other evidence shows a player with an Oddish as a Buddy Pokémon receiving Sun Stone twice after switching. As a result, it might indicate that the case is possible.
However, several users posted that they still receive multiple evolution items even with a Buddy Pokémon that does not need special items to evolve. It caused other Silph Road users to wonder if a buddy Pokémon really affects the drop.
There are many posters in the forum stating that they have buddied up Pokémon that need evolution items but had not seen any drops. For instance, one player posted that he walked with Scyther and got a single Sun Stone, which indicates that buddy Pokémon is not tied to the drop. Some also posted that they are walking with Scyther as buddy and still no Metal Coat drop.
Apparently, the case remains unclear since there are no concrete data to justify itself. Furthermore, it is tough to make a conclusion whether which side of the coin is correct. However, there is no cost in trying to buddy up with a Pokémon, which needs a particular evolution item if players need one.