What you need is a searchable newspaper archive from the mid 1950's to the mid 1960's. Unfortunately, I don't have access to any but the NY Times, which indexes several articles mentioning Mr. Joshua, but only in the late 1960's.

Here's some basic info to get you started; more intensive web searches will probably turn up more.

http://www.caricom.org/uwi%20project/web%20page%20-20may%202003/ebenezer_theodore_joshua.htm

EBENEZER THEODORE JOSHUA
23rd May 1908 – March 1991

Ebenezer Theodore Joshua was founder and leader of the People's Political Party (PPP) of St. Vincent. When he died in March 1991, he had dominated the politics of St. Vincent for more than forty years.

Born in 1908, he was educated at Kingstown Anglican School and by correspondence at the Chicago School of Science and Physics. Mr. Joshua then taught at schools in St. Vincent, Trinidad and British Guiana.

He first entered the political arena as a candidate for the Uriah Butler Party in the San Fernando Legislative Council General Election in 1950. Mr. Joshua then returned to St. Vincent in 1951 and founded the Federated Industrial and Agricultural Workers' Union (FIAWU) of which he was President at the same time as he held the leadership of the PPP. He was elected to the Legislative Council of his own country as a member for North Leeward in 1951. In 1957, he was elected to the Legislative Council but this time as a member for Central Windward and appointed Minister of Trade and Production. In 1960, Mr. Joshua was appointed Chief Minister and Minister of Finance, and retained this post for three consecutive terms. In 1972 he was appointed Deputy Premier.

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http://www.state.gov/r/pa/ei/bgn/2345.htm

POLITICAL CONDITIONS
The People's Political Party (PPP), founded in 1952 by Ebenezer Joshua, was the first major political party in St. Vincent. The PPP had its roots in the labor movement and was in the forefront of national policy prior to independence, winning elections from 1957 through 1966. With the development of a more conservative black middle class, however, the party began to steadily lose support, until it collapsed after a rout in the 1979 elections. The party dissolved itself in 1984.