One source would be the World Bank, specifically the World Development Indicators, although it doesn't look like there's much information pre-1980.

The OECD appears to have information going back to the mid-1970s.

Edit to add this -- These data sources will also give you information about the % of population in poverty and the proportion of national income held by the top and bottom 10% of the population in a given country.

If you're still having trouble, feel free to submit this to /r/Economics. The fine folks there may be able to help you out as well.