national holiday calendar for Apple products

Assuming you mean US Holidays, I've struggled with this one. I use Fantastical in coordination with Apple Calendar. Having compared Holiday Calendars from Fantastical, Google, and various other subscriptions, I always return to the default Apple "US Holidays" Calendar in OSX for my preferred list. It's a setting enabled in the Calendar app:

View Holidays calendar on Mac - Apple Support

Use the Holidays calendar on iPhone - Apple Support

What I struggled with was that I couldn't find the default "US Holidays" calendar in iOS on Fantastical, though it appeared in the Calendar app. My solution was to right click the US Holidays calendar in OSX Calendar, under "Other" Calendars, select "Get Info" and change the Location to iCloud. Once it was in the cloud, I could access it from Fantastical.

More information than you asked for, but maybe it'll help others.

Hello amorah144,

Thank you for using Apple Support Communities. Apple already includes Holiday calendar on Mac. The Holidays listed in the calendar app align with your computer's region. This resource does explain more on how to view Holiday calendar on your computer and how to edit it: View Holidays calendar on Mac - Apple Support

We hope this helps. Thank you for using Apple Support Communities. Take care.