You can do this in a loop:
Dim i as Long, a As Long
Dim shp as Shape
Dim pres as Pres: Set pres = ActivePresentation
For i = 1 to 44
Set shp = pres.Slides(2).Shapes("B" & i)
If shp.TextFrame.TextRange.Text <> "A" Then
aCount = aCount+1
End If
Next
If aCount = 0 Then
MsgBox "No A's were found"
Else:
MsgBox aCount & " A's were found"
End If
Note: This checks to see if the text is "A", not whether it contains the letter "A".