Welcome to the forum! This is really interesting, one of my best friends just found out he has a sister in Viet Nam, same situation as your father. He hopes to meet with her soon. I wish you alll the best on your quest, sorry i can't help.

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This is a pair of Dutch resistance crystal radios, built into a small metal can, and a matchbox. The image is from a postcard bought at a Dutch Resistance Museum in Amsterdam. The matchbox is marked in Swedish, but Swedish matches were sold in Holland for many years..
Scott