There is only one 50mm f/1.0 lens in production today. It is the legendary Leica f/1.0 Noctilux, which is also the fastest rangefinder lens IN THE WORLD. Cue Tenacious D. You can pick a Noctilux up new for, oh, about $6,000. But you’ll need an M-series Leica to pair it with.
Another 50mm f/1.0 lens you can find with a little scouring is made by Canon. This one works with the EOS system, and has been out of production for a few years. This thing also retails for about 5-6k.
Check it out here.