Can you fit a new handle? - Yes
How do you fit a new handle? - Put the new handle on tightly
Where do you obtain a new handle? - Not possible
What options do you have?
Either buy a new set of shears or find a way to fix the existing handle back onto its prong - some low level creativity will be called for - epoxy glue - wooden wedge et cetera...
Good Luck..., August 2015