Integrate Excel VBA Progress Bar into Existing Macro

I'm trying to integrate a VBA Progress Bar into an existing macro, which takes about 5 minutes to run, so that the end-user knows that the macro is progressing. I have a userform with a progress bar designed, but I'm stuck as to how to make it run, showing % complete while the macro is running.

In short, I have a workbook of 300+ clients, each with their own named worksheet. The macro builds an index of all their names, based on the worksheet name, as follows:

Sub ListClientDataSheets()

Sheets("Client Index").Select
Application.ScreenUpdating = False
Application.Calculation = xlCalculationManual
Application.EnableEvents = False
Application.DisplayAlerts = False

'Unprotects the Client Index worksheet
ActiveSheet.Unprotect ("xxxxxxxx")

If MsgBox("Please wait while the Client Index is compiled..." _
& vbCrLf & vbCrLf & "This may take up to 5 minutes, depending on" _
& vbCrLf & "the number of Clients stored in the database" _
& vbCrLf & vbCrLf & "Click OK to continue or Cancel to abort", _
vbOKCancel + vbInformation, "Compiling the Client Index") = vbCancel Then Exit Sub

'Unhides the first 9 non-client (performance) sheets and clears the existing index
Rows("1:9").Select
Range("A9").Activate
Selection.EntireRow.Hidden = False
Range("B1").Select
Range(Selection, Selection.End(xlDown)).Select
Selection.ClearContents
Range("B1").Select
ActiveWindow.SmallScroll Down:=9
Application.ScreenUpdating = True
Application.ScreenUpdating = False

'Sorts the existing Client sheets alphabetically by calling the SortDataSheets macro
SortDataSheets
Sheets("Client Index").Select
Application.Calculation = xlCalculationAutomatic

'Compiles the list of all the worksheet names
Dim Index As Worksheet
Set Index = Application.ActiveSheet
For i = 1 To Application.Sheets.Count
Index.Range("B" & i) = Application.Sheets(i).Name
Next i

'Hides the first 9 worksheet names (performance), leaving only the Client names visible
Rows("1:9").Select
Selection.EntireRow.Hidden = True
Range("B10").Select
Application.ScreenUpdating = True

'Re-protects the Client Index worksheet
ActiveSheet.Protect DrawingObjects:=False, Contents:=True, Scenarios:=False, AllowSorting:=True, Password:="xxxxxxxx"

MsgBox "Thank you for your patience... the Index is now complete!", vbInformation

Application.EnableEvents = True
Application.DisplayAlerts = True
End Sub