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📍 Vigift Da Nang
They have a totally awesome variety of numerous pins about Vietnamese cities - the best choice I've ever seen in Vietnam, you can even buy pins in advance here! See photo: https://maps.app.goo.gl/paKe7Q1kzUXweAQs9.
I found pins from at least those cities or locations there: Can Tho, Nha Trang, Hue, Vung Tau, Try Minh, Ninh Binh, Hoi An, Phu Yen, Bac Lieu, Ho Chi Minh, Ha Giang, Phan Thiet, Quy Nhon.
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📍 Danang Souvenir & Stationery
Shop which has one of the best selection of pins in the city - numerous pins about Vietnam, some about Da Nang and Hoi An.
See photos of all the choices there: https://maps.app.goo.gl/VJmY2fsd2rpcWYtb8 and https://maps.app.goo.gl/JgjktAabShbnjF8R6 .
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📍 Han Market
At least four different shops in this market sell different pins about Vietnam, and some even sell small pins about Hoi An in a form of green lantern - but it seems there is no Danang pins here. See photo: https://maps.app.goo.gl/RoBLdatrCq1QqU1Q8
Pins are quite basic here and of a poorer quality, asking price is 50k.
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📍 Son Tra Night Market
Among all of the souvenir shops on this market (where all sell the same stuff basically) - there are at least two where you can find some pins about Vietnam - with flag or a scooter rider designs. Most shops there don't sell any pins. It's not really possible to pinpoint those shops exactly - so you'll have to look (didn't take much time though).