You could try to use Finturest - Holiday API, it costs 110$ per year. It supports 115 countries and 6 holiday types.

Endpoints:

• GET /v1/holidays/{countryCode}/upcoming

• GET /v1/holidays/{countryCode}/search/date/{holidayDate}

• GET /v1/holidays/{countryCode}/search/year/{year}

• GET /v1/holidays/search/date/{holidayDate}

Example of response:

[
  {
    "date": "2025-06-08",
    "name": "Pentecost",
    "localName": "Zielone Świątki",
    "nationwide": true,
    "country": {
      "name": "Poland",
      "alpha2Code": "PL",
      "alpha3Code": "POL",
      "numericCode": "616"
    },
    "subdivisions": [],
    "types": [
      "Public"
    ]
  }
]

Links:

Holiday API reference

Official Holiday API SDK