Be cautious of sites offering NSP downloads for free. These are often used for "jailbroken" or modded consoles, which can lead to your Nintendo Account being banned from online services or expose your system to malware.

Once you find it, you can buy it using your Nintendo Account funds or a credit card. A Note on "NSP" Files

When you download a game from the eShop, your Switch is technically installing an NSP file.