после долгих потягиваний и совершенно бесполезных комментариев я нашел решение:
Dim unitstring As String() = Split(TextBox2.Text, "\") 'separate directory names
Dim unitcount As Integer = Array.LastIndexOf(unitstring, Path.GetFileName(TextBox2.Text)) + 2 'get how far in the directory we are from the root.
Dim paths As New List(Of String) 'list to hold results
For Each x In IO.Directory.GetDirectories(TextBox2.Text, "*", SearchOption.AllDirectories) 'loop through all directories to get them in the format needed
Dim pathsplit As String() = Split(x, "\", unitcount) 'split from parent
paths.Add(pathsplit(unitcount - 1)) 'the last item in the array is what is needed.
Next
, если кому-то еще нужен такой код, не стесняйтесь его использовать.