Where to find dealers with a mask of a dragon? (Sekiro: Shadows Die Twice)

What is this mask necessary ? I do not know.

PROTOTYPE XOF
change glasses boost the force of impact , you need to collect (buy) 3 parts from vendors around the world games

all he found

APELCIN
how much points for 1 increased strength?

MrShiro20
Five, I think.

APELCIN
where's the rest?

KATAMARAH
two parts two merchants in barrels (one in flashback , the other in locations with carp (forgot the name) ) , part 3 is also Tolosa which is sitting beside the idol in an underground secret course
read it here
Спойлерhttps://ru.ostrog.com/sekiro-shadows-die-twice-24054/