There are a few different posts in the community with examples of how to calculate network days in Tableau. Re: Calculating Networkdays with Tableau and Is there a efficient way to find out networkdays in tableau? are a couple. Do these provide the details to help you accomplish this directly in Tableau?
I cannot help you with the Access nor the VB Script, but I can point you to an article that shows you how to calculate business days (networkdays) in Tableau.
This article has a workday attached that that demonstrated how to do it. No Access nor VB needed.
You can copy and paste the code into your own calculated field. This example calculated business days on a monthly basis, but you can adjust it to a year.
PS. This example assumes that you take August off for vacation :-)
Hope this helps a bit, -Birgit