According to the explanations given in Wiki.

This seems also to match with the one given by Citybank Japan (see the link below, page 2)

Hoping this will be some kind of help

I think “ゴロ” is another expression of “ごろつき” which is hoodlum, rascal, ruffian, villain, etc. Apparently they are the members of a gangster organization in Japan. Also, I do not think there is a definite Japanese translation for this term. So, you have no choice but to come up with a proper translation.　
HTH

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Note added at 1 hr (2010-05-12 19:10:29 GMT)
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Oops, 何と政治団体だ！となると、こう訳しておきましょう。
hoodlums/black-hearted crusaders belonging to an officially registered political organization seemingly advocating social movement

I agree with Alain C. Bourbonnaud's opinion as well, also by looking at the Wikipedia's definition.

It's basically a local political organization made up of ex-Yakuzas, commonly those who had been forced to be liquidated by the anti-organized crime law. They do not actually get involved in political activities but engage in organized crimes such as fraud just like normal mafias would.

ごろつきis defined in the Shogakukan Dictionary as: a homeless and jobless hooligan; [ゆすり] an extortonist; [米」a racketeer
I've based my answer on the following article about organized crime in Japan regarding these types of "yakuza" and the definition of "Minbo" which was in your Wiki site:

http://www.asiaquarterly.com/content/view/119/40
Second, organized crime syndicates have been expanding their financial activities beyond traditional means such as gambling and prostitution to include what is known as minji kainyu boryoku, literally “violent intrusion into civil matters.” Minji kainyu boryoku, or minbo for short, has been defined by the police to include the following: debt-collection; corporate extortion (sokaiya); finance-related incidents; bankruptcy management; real-estate and rent-related problems; settlements of traffic accident disputes out of court; disputes over prices of goods and other everyday matters; and other civil disputes. Another financial activity of the yakuza that impinges on the lives of non-yakuza is land-sharking (jiage), through which owners of small plots of land are coerced into selling their property so as to create a larger development site. Coercion can take the form of threats, the driving of cars into the plot of land, arson, and loud disruptions at night. Land-sharking was the largest source of income for yakuza syndicates in the Kansai (Osaka-Kobe-Kyoto) and Kanto (Tokyo-Yokohama) areas during the bubble economy.9