There are 3 ways to get a nib that flexible:
1. Buy one of Lou's gold nibs and grind the sides of the tines with a Dremel stone to make them as flexible as you want. You can do it with Lou's steel nibs, but the steel is less flexible than the gold.
2. Buy one of Lou's nibs and send it to one of the custom pen guys and pay to have them do it. It was about $75 last time I looked.
3. For $400 you can buy a Namiki fountain pen with a super-flexible nib that comes ready to write just like that.
Should you do this, BE CAREFUL. Those flexible nibs bend easilly.