Here's a group I didn't know about until today -- the Unrepresented Nations and Peoples Organization (UNPO). It is a democratic, international umbrella organization of indigenous peoples, occupied nations, minorities and independent states which do not enjoy diplomatic representation internationally. UNPO acts to educate, to mediate disputes, and to advocate for human rights and for recognition by the nations of the world. Though members appear to come mostly from developing and former communist regions (see map above, click to enlarge), there are groups like the Lakota Nation which reside in developed countries, in this case the U.S.
I wish them well. Here is UNPO's flag.