You could run the Hebcal CLI (command-line interface) as part of your powershell script and capture the output into an environment variable.

https://github.com/hebcal/hebcal

The Hebcal CLI is written in Go, so it's cross-platform and should compile/run just fine on Windows.

Here's what it looks like on Linux/macOS -- should be the same on Windows

Hi, thanks for using Hebcal.

You can download a CSV file with Rosh Chodesh dates that you can modify for your purpose

1. Go to https://www.hebcal.com/hebcal

2. Uncheck all boxes except Rosh Chodesh

3. Click Create Calendar button at the bottom of the page

4. On the next page, click Download

5. Click CSV at the top of the download dialog box, the click the grey Download CSV button

6. Modify the CSV file in your favorite spreadsheet app as you see fit

Tisha B'Av is the Ninth of Av. It is a fast commemorating the destruction of the two Temples.

Tu B'Av is a minor Jewish holiday of love. It is observed on the 15th day of the Hebrew month of Av.

This article describes how to make changes to a Yahrzeit + Anniversary calendar that you downloaded, exported or subscribed to in a calendar app like Outlook, Google Calendar / Android, or Apple (iOS, iPhone, iPad or Mac). These instructions apply to personal events such as yahrzeits, Hebrew Birthdays, and Hebrew Anniversaries.

How to make changes to a Yahrzeit + Anniversary calendar

https://www.hebcal.com/home/632/how-to-make-changes-to-a-yahrzeit-anniversary-calendar