Hi Kubilai,
Norgate Data offers information regarding historical index membership to subscribers to our US Stock service (at the Platinum level or above) who are using a supported backtesting/analysis platform such as AmiBroker, RealTest, Wealth-Lab or Zipline that is linked to our database. Even then, access to the information is only indirect - for instance, index membership can be stipulated as a buy condition in a system test. There is no calendar or list showing historical additions to, or removals from, an index.
We cover Russell 2000 constituents back to July 1990, comprising of over 10,000 companies that were in the Russell 2000 at some stage or are currently in the index.
Which backtesting/analysis platform do you use?