A patched ROMs pack implies that the ROMs have been modified or updated to fix bugs, improve compatibility, or add new features. Patching can also involve fixing issues related to region-locking, language support, or other regional differences.
You can try searching online repositories, forums, or communities focused on retro gaming and emulation. Some popular sources include:
While emulators are legal, downloading commercial ROMs is copyright infringement (US, EU, Japan). Downloading a "pack" is worse than downloading a single ROM because it implies willful mass infringement. ISPs and copyright trolls specifically monitor torrents containing "Nintendo ROM packs."