It really depends on what you want to make it out of. Some people have made a P1 bio from a pepekura [all a scar bio really is is a P1 bio with the marking on it's head]. Some people have sculpted the bio, molded, and cast it.
Here's a link to propzone. You can purchase a pepekura AVP bio file for $15.
i have been having the same problem with pep files, you could just cut a circle out of card board and cut slits in it then tape and it will be more dome like, then u can cover it with car body filler or somthing like that. it works for some peaple, i did somthing close by coverig the card board with alot of masking tape then painting it like 7 layres of acrylicand enamal, worked out fine for meC:\Users\Massey\Pictures\henrymassey\124.JPG