Mementos unlocks on 5/7, following Kamoshida's confession at Shujin. The first Mementos Request is part of the storyline, but ...

To get the Wizard's Hat in Megabonk, players will first have to get their hands on Vlad and the Pot (stainless steel).

Those are all the Relics you can find in Hollow Knight Silksong. It's easier to find them if you know where to get all the maps from Shakra, plus how to navigate The Mist so you can reach the Citadel ...

There are various ways of getting gear, but outside of raiding, exchanging your hard earned Tomestones if the best.