an ideas:
the most conservative approach is to use a cost basis of zero - no one can argue with that.....if the stock price 10 years ago was very small, might as well use zero as the tax difference could be minor
where was the stock held? does that firm have any records? most financial institutions hold these records for years and years.
did you have the stock certificate? was there a date on it?
do you have old tax returns were the dividends were reported? if so, you know it was owned for that long.
