I don't think you can use{3} for your needs. I can't answer your exact question but I use this macro for finding strings that aren't always know.
Code:
Sub WhereIsIt()
a1 = "[0-9A-z] "
B2 = "Z[0-9A-z]Z"
ActiveDocument.Range(0).Select
Selection.Find.ClearFormatting
While Selection.Find.Execute(a1)
StartReformat = Selection.Start
Selection.MoveRight
Selection.Find.Execute (B2)
StopReformat = Selection.End
Selection.MoveRight
Selection.Select
Selection.Font.Color = 255
Selection.Font.Bold = True
Selection.Font.Size = 20
Wend
End Sub