UPDATE: The Sinai Peninsula needs to be included as well.
On a national level, no country reaches the high number of 20% rh negative people, even though Australia is close with 19.5.
The Berbers
There are only 2 reports available according to which the percentage of some Berber tribes (namely the Ait Haddidu Berbers in the Atlas mountain region of Morocco) have a percentage of rh negatives reaching as high as 40%
The Basques
Around 35% of Basques are rh negative in the higher regions. The Basques are located in the Pyrenees mountain region of Spain and France. Basque ancestry has been traced to the Sumerian region based on genetic examination of ancient burial grounds and in terms of similarity of languages.
Scotland
The region with the highest known rh negative people´s frequency of 30% is Inverness on the west coast. Other regions with more than 20% rh negatives in Scotland include Oxnard and the Isle of Mull.
Northern Ireland
Northern Ireland´s numbers have recently been published and the values are at 27% rh negative people.
Rhoney Valley, Switzerland
The towns of of Tenna, Versam and Safien in the Rhone Valley in Switzerland show a frequency of the rh negative gene of 0.515.
That would make the percentage of rh negative individuals 26.5%.
More here: Blood types of the Walsers
Bunschoten-Spakenburg, Netherlands
This Dutch municipality with 20,000 inhabitants houses 25% rh negative people.
Catalonia
20% of Catalonians are rh negative.
(See also: GRUPOS SANGUÍNEOS EN CATALUÑA )
So what else do these areas have in common?
1) Except the Atlas region, these areas are all by the sea. Most are in mountain regions. This could easily be due to migrants settling in a region where they felt protected by the vicinity and surroundings.
2) The Celtic marker R1b is listed as being most frequent in North West Ireland, Scotland, within the Basque and Catalonia region and in the Netherlands.
There are two exceptions:
Berbers are not anywhere close to the list of highest R1b frequencies and another population with a high percentage of R1b carriers, the Welsh, don´t seem to check out high for percentages of rh negatives.
3) 5 of the 7 populations listed are well-known for seeking independence from the countries they are a part of.
Aside from the above regions mentioned, a study from the 1950s examining a little bit more than 100 Karaite Jews revealed an rh negative gene frequency of 0.53 making the percentage of rh negative within that group somewhere around 28%.
Another group worth mentioning are the Guanches of the Canary Islands.
However, as a tribe they are considered extinct as the vast majority of their current gene pool comes from elsewhere, to a great part Basques and Berbers who once came to the Canary Islands.
See also:
Where is rh negative blood most frequent?
Blood Type Frequencies by Country including the Rh Factor
Blood Type Frequencies by Regions, Tribes and Ethnic Groups including the Rh Factor