ﾌｧｲﾙの件数は最高で99件です
01-99

こんな感じでどうでしょう｡
"C:\test\" にあるCSVﾌｧｲﾙのみを連結して､"C:\test\test.csv" に出力します｡
ﾀｰｹﾞｯﾄのﾌｫﾙﾀﾞ､拡張子､出力先ﾌｧｲﾙ名は､ﾏｸﾛの最後の Call hogeCoupling の引数を変更することで対応できます｡

Option Explicit

'1ﾌｧｲﾙ処理
Sub appendFile(path As String, fname As String, outfname As String)
 Dim buf As String, idx As String
 Dim fname2 As String, fname3 As String
 Dim x As Long
 
  'CSVﾌｧｲﾙ読み込み＆書き込み
 fname2 = path & fname
 Open fname2 For Input As #1
 Open outfname For Append As #2
 Do Until EOF(1)
 Line Input #1, buf
 Print #2, buf
 Loop
 Close #2
 Close #1
End Sub

'ﾌｧｲﾙ探索＋処理実行
Sub hogeCoupling(path As String, ext As String, outfname As String)
 Dim fcol As Object, re As Object
 Dim flist As Variant, remat As Variant
 Dim pat As String, fname As String
 Dim n As Long
 
  '処理対象ﾌｧｲﾙ探索＋処理実行
 Set fcol = CreateObject("Scripting.FileSystemObject").GetFolder(path).Files
 Set re = CreateObject("VBScript.RegExp")
 pat = "\." & ext & "$"
 With re
 .Pattern = pat
 .IgnoreCase = True
 .Global = True
 For Each flist In fcol
 Set remat = .Execute(flist.name)
 If remat.Count > 0 Then
 Call appendFile(path, flist.name, outfname)
 End If
 Next flist
 End With
 Set re = Nothing
 Set fcol = Nothing
End Sub

Sub main()
 Call hogeCoupling("C:/test/", "csv", "C:/test/test.csv")
End Sub