I too use a hand-coping saw for all G-10 rough cuts without issue. Just takes some elbow grease. Sure, 3/8 would be tougher.... but.,.. I think doable as str8fencer suggests.
Too bad about the mis-order -- I just ordered $35 worth of G-10, thinking WOW why is it so cheap... ordered all .012 thinking it was .12
On the bright side.. I just picked up all sorts of colorful liners. Haha. Decided not to send back.