Public Sub X()
    Dim firstAddress As String
    Dim c As Range
    Dim X As String
    Dim strAddress As String
    
    X = "a"

    With Worksheets( 1 ).Range("A:A")
        Set c = .Find(X, LookIn:=xlValues)
        If Not c Is Nothing Then
            firstAddress = c.Address
            strAddress = firstAddress
            Do
                Set c = .FindNext(c)
                strAddress = strAddress & "," & c.Address
            Loop While Not c Is Nothing And c.Address <> firstAddress
        End If
        
        .Range(strAddress).Select
    End With
End Sub