Hi all sifu in mod

How to make/mod the case fan to an USB fan? Most fan come in 12v while the usb is only rated at 5v, result is the usb+case fan mod is slow or even dont move. (especially 120mm and above fan haha).

My questions
1) is there a 12v usb?
2) 5v fan max size is only 40mm, any bigger?
3) How to make the usb+case fan move faster?

Thank you all