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

Thanks for the suggestion!

Do you have a reliable source (online or offline) that you can send which includes a complete list of the Haftarot that have special chanting?

A quick internet search reveals this page, but I don't know if this is accurate and/or complete:

https://stephanieshore.com/haftarah/haftarah-special/

Hi, please try these instructions which should also work for Outlook 2021 for Windows 

https://www.hebcal.com/home/8/outlook-ics-jewish-holidays

Hi, thanks for your message. Sorry to hear that you are having difficulty accessing hebcal.com. According to our automated monitoring the website is running fine. We did a manual check and can't find 502 error messages.

Can you post a screenshot?

The Alternate Haftara are used by some conservative congregations.

Haftarot for a Triennial Cycle Torah Reading

http://www.rabbinicalassembly.org/sites/default/files/public/halakhah/teshuvot/2011-2020/triennial-haftarot.pdf

Great, glad to hear that worked for you.

If you wish to download dates further into the future, go back to the custom calendar page (step 1 above) and enter a year further into the future (for example 5787) and repeat the process. Each time you'll be able to download a 10-year CSV file.

Hi, thanks for using Hebcal.

From reading an article that Microsoft posted, I believe it's possible to use Unicode characters in a folder name

https://learn.microsoft.com/en-us/windows/win32/intl/character-sets-used-in-file-names

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

We've added a feature for IFTTT and other APIs where you can append ?yto=1 to a Hebcal URL so the events that show up are only yom tov holidays.

For example:

https://download.hebcal.com/v4/CAFAAWoBc4ABAZgBAaABAQ/hebcal.ics?yto=1

For Gregorian year 2023, for example, only the following holidays would be considered Yom Tov:

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.