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Dear Mr. Gorball,
Thank you for posting your request on History Hub!
General information on the Ka-Bar can be found here: https://en.wikipedia.org/wiki/Ka-Bar.
As for Marine Corps Shoulder Insignia there are plenty of websites that discuss the history of the Marine Corps should insignia and why the Marine Corps band their use. A good place to start is here: https://www.marinecorpstimes.com/news/your-marine-corps/2018/05/14/the-time-the-corps-wore-shoulder-unit-patches/
There might be information about iconography and the meaning behind the leaf and ka-bar on the insignia with the Commandant Correspondence or the Correspondence of the 2nd Marine Division in the Records of the U.S. Marine Corps (Record Group 127).
We hope this is helpful. Best of luck with your research!