rue montgallet still exists in Paris. Yes, very less than it used to be, but still there.
https://m.youtube.com/watch?v=Xjj6uIIUT_0 gives a good idea of how it is now
https://m.youtube.com/watch?v=Xjj6uIIUT_0 gives a good idea of how it is now
But, I guess, if you need a mouse right now and don't insist on the absolute best price, they're still there, yeah.
In practice, I live two streets away from there and yet I do all my shopping online (not that I buy that many parts anymore).