Here are Vincent Valentine's arm and hand armor
It may need to be scaled to fit your arm and hand. I'm a pretty average build with average size hands, so it might be a nice base to start.
The arm.stl also has the elbow part in the file. That's how I printed it, so you can ignore the single elbow.stl if you want.
To attach all the arm pieces together, I ran strips of craft foam between the sections. That way it would flex when I need it to, but also stay pretty rigid.
Have fun printing these!