It's become pretty strict due to legal concerns, but there was a shop that was giving out access to new accounts during their anniversary event recently so that could be something to look out for. I think Neko's homebrew store is still available to add onto Tinfoil but you likely won't find official games there.

If you're lucky enough to have some missing DLC though, then definitely feel welcome to contribute to preservation efforts.

There are sites where you can download the game files and install via tools like Goldleaf or Tinfoil. Both seem to support installation over USB cable, so you just have to connect it to your PC and run the tool to install things.