White Dye Merchant - Just West of the Wanderer's Pass on the map in Izuhara, at the top of a mini mountain, near a bamboo strike in North-East Kashine in the first region.
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https://1drv.ms/u/s!Ag4k9wJMk2ebkfFy8kaYG1YWqTNEhw-
https://1drv.ms/u/s!Ag4k9wJMk2ebkfFzuxqr-vaT8jA2Hw-
https://1drv.ms/u/s!Ag4k9wJMk2ebkfFxPPbgaDMUlcPSEQ Black Dye Merchant - The Eastern part of the Toyotama region, between Urashima's Village on the coast and Kawamata Village (it's much closer to the latter), which is North of the Yarikawa Stronghold. He is hanging out in a cave in a bamboo forest.
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https://1drv.ms/u/s!Ag4k9wJMk2ebkfF1DW9O8euQTiGFmA-
https://1drv.ms/u/s!Ag4k9wJMk2ebkfF0STSskU0CfboPOQ-
https://1drv.ms/u/s!Ag4k9wJMk2ebkfF2BaKNSX711WO_XgBuy 1 item from each (for 5-10 flowers), then the trophy will pop.