How do you complete cost basis calculations if you don't have the information from a deceased family member

If you inherited the stock then the basis is the market value as of the date of death which is easily found on the web.  

You need to post more details. Are you preparing the return for the deceased family member or yourself as donee or legatee (i.e., for property you were gifted or inherited).

Did you inherit (or otherwise acquire) property from the deceased family member, was the property gifted (in whole or in part) to you, et al?

Property acquired from a decedent is generally stepped up to its fair market value on the date of death of the decedent.