Any figure with a basic flying suit (coveralls, essentially), Mae West,
parachute, and flying helmet (which is just a soft hat that covers the
entire head) with goggles should suffice. Most Monogram kits provide
one for the cockpit in thier WWII fighter kits, and some of them are
actually not bad figures, while others kind of suck. Some come with
standing figures in the same gear. The pilot and co-pilot figures that
come with the B17G kit could work, though they're wearing A-2 leather
flight jackets. But that could be plausible, since those jackets were
pretty universally popular, no matter the theater of operations.
My suggestion would be to grab a book or two, with pictures of
what pilots looked like, either in general, or in the specific theater
of operations you're modeling, and either look for figures that have
the right gear, or use what you've learned from your books to modify a
figure to have the right gear.
If you're not up to the modification work, check with the aicraft
modelers. I'm sure that if they can't hook you up with some figures
from their scrap boxes, they can certainly point you in the right
direction.If I had any, I'd be happy to part with them, but I don't. I
suppose I could make one for you, if worse came to worse, but there's
plenty out there. Check the kits at your LHS too. There's usually pics
on the side that show the finished model on the side, along with the
figure.
Perhaps you don't want to blow the money on a kit just for one
figure. Understandable, but you're just not a kit builder until you've
spent $32 on a Sherman tank kit, just for a set of idler wheels and a
turret.
This book may be of some use.
http://www.amazon.com/gp/product/1855325306/ref=nosim/102-1069570-1776921?n=283155
All Opsprey books have great color plates showing people and/or
vehicles. This one, I've not seen up close, but I have about a hundred
of these books in my library, and they're all the same, so I'm sure it
has several useful color plates in it.
Also, Google USMC aviators in WWII, and see what you find.