VBA: Searching For Specfic Terms

I'm writing a macro to search for letters A to Z in one spreadsheet, and copy it's associated data into another spreadsheet where A to Z already exist.

Thus:
Cells.Find(What:="A", After:=ActiveCell, LookIn:=xlFormulas, _
LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:=xlNext, _
MatchCase:=False, SearchFormat:=False).Activate

That works fine. It find's "A", then the rest of the macro moves to the right and copies the data needed:

ActiveCell.Offset(0, 1).Range("A1").Select
Range(Selection, Selection.End(xlToRight)).Select
Selection.Copy

THEN it goes to the NEW spreadsheet (where A to Z are already labeled) and pastes into the corresponding area. Thus:

Windows("The Other Sheet.xls").Activate
Cells.Find(What:="A", After:=ActiveCell, LookIn:=xlFormulas, _
LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:=xlNext, _
MatchCase:=False, SearchFormat:=False).Activate

ActiveCell.Offset(0, 1).Range("A1").Select

Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
:=False, Transpose:=False

This works perfectly.

However:

What if, one day, "A" does not exist in the source data? If say, the data started at "B", because there were no results for "A". Currently, the macro will stop working if it attempts to search for a value that doesnt exist.

How do I make it, for example, Search for "A", find that "A" doesnt exist, then skip to Searching for "B", and then "C" and so on?