1099-b cost for pre-2011 stocks

I just open google and type  "Historical stock prices for Company name" and hit search.

I use this one

https://www.marketwatch.com/tools/quotes/historical.asp

--just used it yesterday to find stepped-up basis for inherited stock sold by widow after husband's death in 2019 (community property).  Lazy "financial planners" are willing to take her $4,000 annual fee but can't do the work themselves. 

These may not be covered securities but the wage reporting requirements were the same for those years.

Before venturing to use public websites to determine your client's cost basis, you should ascertain what kind of options those are.  Statutory options are treated very differently from NQSO.

It's best to go back to the returns filed for those years as well as the related W-2s, comp breakdown, and stock options documents from that time.  Historical trading prices do not establish basis.  What was, in fact, previously reported as your client's gross income does and the burden of proof is on the taxpayer.