Where To Buy Korea Occupation Stamps

I'm trying to find a set of stamps issued in 1950 during the North Korean occupation of South Korea. My Minkus Supreme album has spaces for a 7 stamp set. The set is not listed in Scott but the lowest three values are listed in Stanley Gibbons (North Korean Occupation of South Korea 1 to 3). More surprisingly, my 1975/76 Minkus catalog also lists only the three lowest values (North Korean Occupation of South Korea 1 to 3).

Can anyone recommend a dealer who might have these issues or some other source so I can fill these spaces?

These stamps are Michel KP-KR 1 through 9. However there is a note that the "authenticity of this stamp is doubted" for KP-KR 4 through 9.