Recently I purchased a cover that I am guessing is from the late 1950s based on the affixed stamp and a possible date of 4292.6.8, so 1959. Unfortunately, my copy of the Korean Postage Stamp Catalogue 2020/2021 does not illustrate commemorative postmarks past 1957. I don’t know if this has changed in later editions of the catalogue.
I have looked through the past issues of Korean Philately from the late 50s and was unable to find this particular postmark illustrated in any of them. This large circular design incorporates the names and flags of several Asian countries including Singapore and Macau, Taiwan, etc… and includes the text 제5차 아시아 … 공대회. Part of this is illegible due to the postmark strike.

I also compared this with commemorative stamps issued from the same time period thinking that it might have been created as a postmark/cachet for a specific set of stamps but could not match anything.

Any information about this postmark would be appreciated.

This postmark has nothing to do with certain commemorative stamp. It is an independent commemorative postmark which exhibits the 5th Asian Anti-communist Nations Congress.
Thanks for your quick answer to this question, Jin Hur. Bob
Thank you for this additional information. Do you know of any images of a more complete strike of this commemorative postmark or do you or our members have examples of this commemorative postmark in their collections that they could share?
I am sorry. As a Korean collector, I have seen this postmark in your article for the first time ever.
What a shame!
Jin Hur, Are there any catalogs or online resources that list or identify all of the South Korean commemorative postmarks after 1957? Also, I found a very good image of the above postmark on eBay.
I remember that such kind of catalogue was once published. But I have no sample at the moment. I will let you know later.
I am sorry that I am now terribly busy in taking care of Philakorea 2025 matters.
Jin Hur, thank you for all of your help with this. I really appreciate it. I was just reading Korean Philatelic News (May 2025) and it is exciting PHILAKOREA 2025 World Stamp Exhibition is coming together. I attended a PhilaKorea exhibition in 1994 when I was living there. My wife and I are traveling to Korea from August 9 to 22. I will be in Busan and know of at least one stamp store there that I have visited in the past. I will see if there is any information about commemorative postmarks at that location. Thank you again for your efforts.
Here is the image from Ebay Darrin refers to:

I have found the catalogue. It was published in 2004 by Korea Post and contains all the commemorative and tourism promotion postmarks of all time. And I have encountered the aforementioned postmark, too, on 64th page. This catalogue was not for sale, that’s why it is a little bit difficult to find in the public market or ebay.
Jin Hur sent the following two photos showing the cover of the catalogue plus the page with the postmark:
0098
제5차 아세아민족반공대회 기념
사용기간 : 1959년 6월 1일 ~ 6월 10일
사용국명 : 서기관국
디자인내용 : 대회장식과 국기에 반공과 창의
디자이너 : 강 박
고 시 : 체신부 공고 제268호 (1959. 5. 29)
0098
Commemoration of the 5th Asian Peoples’ Anti-Communist Conference
Period of Use: June 1, 1959 – June 10, 1959
Issuing Office: Seoul Central Post Office
Design Description: Conference emblem and national flags symbolizing anti-communism and creativity
Designer: Kang Park
Official Notice: Ministry of Communications Notice No. 268 (May 29, 1959)
Jin Hur’s listing gave me an idea: would this postmark be in the online catalogue KoreaPost created for stamps and cancellations and such? Quick search and yes, there it is: 제5차 아세아민족반공대회 기념
This is the image KoreaPost used:
And here is the text from that page, with a translation below:
제5차 아세아민족반공대회 기념
날짜도장종류 기념우편날짜도장
디자인 대회참석국 국기에 방패와 창
디자이너 강박
발행일 1959. 6. 1.
사용우체국 서울중앙, 서울국제, 광화문, 서대문, 용산, 영등포, 인천, 수원, 춘천, 강릉, 대전, 청주, 부산, 대구, 김천, 마산, 진주, 포항, 진해, 광주, 전주, 군산, 이리, 목포, 순천, 여수, 제주
사용기간 1959. 6. 1. ~ 6. 10.
Commemoration of the 5th Asian Peoples’ Anti-Communist Conference
Type of Postmark: Commemorative Postmark
Design: Shields and spears over the national flags of participating countries
Designer: Kang Park
Issue Date: June 1, 1959
Post Offices Used: Seoul Central, Seoul International, Gwanghwamun, Seodaemun, Yongsan, Yeongdeungpo, Incheon, Suwon, Chuncheon, Gangneung, Daejeon, Cheongju, Busan, Daegu, Gimcheon, Masan, Jinju, Pohang, Jinhae, Gwangju, Jeonju, Gunsan, Iri, Mokpo, Suncheon, Yeosu, Jeju
Period of Use: June 1, 1959 – June 10, 1959
This is great! I had no idea Korea Post had this stamp gallery that also included postmarks. This will be a really good resource. Also, thank you Jin Hur, for the photo of the book. This is something I will seek out when I am in Korea later this year in August visiting family.
If I find out personally, I will report to you.