Need authoritative source for historic Bitcoin conversion prices from all exchanges What are the authoritative sources for historic Bitcoin prices? 

Ideally this will be an API for all major exchanges.
All historical data from any exchange available at Bitcoin Charts: Markets API


  Historic Trade Data
  
  Trade data is available as CSV, delayed by approx. 15 minutes. It will return the 2000 most recent trades.
  Format:
  
  https://api.bitcoincharts.com/v1/trades.csv?symbol=SYMBOL[&amp;start=UNIXTIME]
  
  Returns CSV with columns: unixtime,price,amount 
  
  Example
  
  Latest Kraken EUR trades:
  https://api.bitcoincharts.com/v1/trades.csv?symbol=krakenEUR