Google Merchant Marine flags for sale. Numerous vendors appear in the search, including Amazon. You could also ask on the Merchant Marine FaceBook page. https://www.facebook.com/groups/MerchantMarinesWWII
Regarding the Navy Armed flag. Looks like this one would need to be custom ordered. Again google "custom flag" and numerous vendors appear. I know for a fact that the AG vets on the SS John W. Brown had several AG flags made. I do not recall where they bought them. I also not 100% sure what the design was. I will look the next time I am onboard the ship. I last saw the flag in the flag locker.
Look for my Navy Armed Guard group on FB.