Okay, here are my attempts and tinkerings with flag shields and roundels I thought would be useful for potential future projects, but which don't (or didn't at the time I may made them) exist in the Civ2 community. Many of them are indeed quite crude by the standards of many other posters here.
The first five rows are historical, and are, in order - Republic of Rio Grande, Yucatan Republic, Zacatecas Rebellion, Tabasco Rebellion (all four during and against the presidency of Santa Anna), Hudson's Bay Company in the early 19th Century, very short-lived "Republic of Canada" in 1837, Orange Free State, Anushilan Samiti (Bengali secret society largely behind February 1915 mutiny and one involved party in WW1 Hindu-German Conspiracy), WW1 Kingdom of Siam (Thailand), Dervish State (de facto independent Somali Sultanate that declared itself allied with the Central Powers and raided British Somaliland), People's Republic of Belarus (1918-1919)/Belarusian Central Rada (1943-1944), Ukrainian Insurgent Army, Lebanon under the French Mandate, a proposed flag for German citizen groups who secretly resisted the Nazis in WW2, Commonwealth of Nations, Four Freedoms Flag (meant for units that lump together a bunch of small "Free <Blank> Forces" units), hypothetical Imperial Japanese protectorate/proxy state/military zone in Western US, hypothetical Imperial Japanese protectorate/proxy state/military zone in Australia and New Zealand, Pro-Axis Iraqi Coup if they and the Axis had been more successful hypothetically, Khmer Republic (between original Kingdom and Khmer Rouge under Lon Nol), Kingdom of Laos, Republic of Egypt (1952-1958), Late Qing Dynasty China, Princely State of Sikkim, Princely State of Hyderabad, the Maldives (which, on reflection, should be in the next category of extant nations no shield flags exist for), Italian Somaliland, Northern Yemen under the Imamate, very short-lived British Eritrea, Colony of Aden, Southern Arabian Federation, Ethiopian People's Liberation Front, Republic of Sudan (1956-1969), Northern Yemen as Arab Republic, Southern Yemen, Djibouti (same reflection as the Maldives), hybrid flag of Lesotho and Swaziland from 1960's and 1970's, Bophuthatswana (one of South Africa's bogus African "homelands" or "Bantustans," but whose defense force surprising handily dispatched an well-funded and equipped Afrikaner militia hoping to exploit the turmoil in the final days Apartheid to claim their own personal kingdom), Movement of Democratic Forces of Casamance, FROLINAT, Taliban, British Hong Kong, Portuguese Macau, Lord's Resistance Army.
The next row is extant nations that don't have flag shield out there I'm aware. They are, in order - Cape Verde, the Gambia, Equatorial Guinea, Sao Tome and Principe, Cote d'Ivoire (Ivory Coast), Ghana, South Sudan.
The next row (and single item below) air force roundels. They are, in order - RCAF in WW2 (that's one of my worst), Mongolian People's Air Force, Royal Lao Air Force, Royal Thai Air Force, Indian Air Force, Pakistani Air Force, Burmese/Myanmar Air Force, Pre-1960's Egyptian Air Force/UAR Air Force/Present-day Syrian Air Force, Royal Saudi Arabian Air Force, Iranian Air Force, Lebanese Air Force, Iraqi Air Force, Post-Cold War Russian Air Force, Afghan Air Force.
And four miscellaneous items - the Seal of the CIA (REALLY should be attached to an Espionage unit

), Indian Navy, IDF 35th Brigade (Israeli paratroops and special forces), Eureka Flag (popular alternative flag of Australia, especially if it declares itself a republic).
Edit - changed "the Gabon" in the list of extant nations to the Gambia