They do indeed exist.  You could get them for free from Galoob back in the day of the top loaders, you just had to mail in a form to them.  They are pretty pricy to get anymore, usually around 30-40 bucks seems like.  I still need one myself in fact.

There are ways to use your GG on a top loading NES, it just looks stupid.  I just a fami converter inside the NES (72-60 pin), then I use a converter from a Gyromite (60-72 pin) next.  Then put the GG in that, then the game.  It sticks out like a foot above the NES but it works

I'm not too concerned with actually using the game genie.  I have a toaster too.  I am mainly looking for one just to have.  It just seems like that would be something cool that most people don't have.