Use World Development Indicators

• Select desired countries.
• Select series, Income share held by highest 20%, Income share held by lowest 20%, etc.
• Select Years. Note that the data may not be available for all countries for all years. Select a wide range of years.

Economist Intelligence Unit: EIU Data Services - Market Indicators & Forecasts

• Open Data Tool from Data tab at the top of the screen.
• Select All Market Indictors & Forecasts from drop-down in Step 1.
• Choose the geography
• Choose the series Income Distribution under Demographics and Income 
• Click the + sign to find the particular series of interest
• Choose the time frame and click on View Data to see results.

See also Economic Report of the President. (US)