Drop Down List hyperlink to sheets in another workbook

To navigate a drop down list with 500 options could be a mission...but maybe this may get you started which is more simple to create. It will generate a list with all the sheetnames and when you double click on a sheetname it'll open that sheet.

Create a sheet with the name SHEETLIST or whatever in your Master Plan and run this code in your Master Plan

Sheets("SHEETLIST").Select
Range("A1").Select

For i = 1 To Workbooks("Stock Plan.xls").Worksheets.Count
   ActiveCell.Value = ActiveWorkbook.Worksheets(i).Name
   ActiveCell.Offset(1, 0).Select
Next

then in your Master Plan's Workbook Module create a SheetBeforeDoubleClick function with the following code

if activesheet.name = "SHEETLIST" then

sheetname = activecell.value
workbooks("Master Plan.xls").activate
worksheets(sheetname).activate

endif