I didn't see anyone offer a vba solution so I did a quick and dirty
code under the "Workbook_SheetSelectionChange" sub to carry the last
closing stock  down to the "current" row.

Here's the logic:
-> click on any cell  on the "Opening Stock" column and if there
exist a previous  item matching the current cell, then it will be
carried down to the activecell. It will also throw in the formula
for the "closing stock" just incase it got deleted...

I didn't know all the specifics, so no error checking is done. You
will have to modify the code to suite your needs.

Download the xls file from here:
http://www.modernfalconry.com/test/Madhu%20Raju%20sales%20file.xls