Hey Burnstribe,
I have the same sort of project going. You should be able to find usable seatbelts from WWII era planes. The bomber seats are mostly repro now... they are actually easy to make. Check out the seats in Back Seat Betty.
I am using all WWII gauges and switches. You can find mechanical warbird gauges on ebay, like oil pressure and Air speed. Some electric gauges are 12 volt, many are 24 volt and won't read correctly. Some require a sender that will be hard to find. You can always get new 12V guts put in an old gauge -but it's not cheap.
Warbird oil tanks and Hydraulic fluid tanks can make good fuel tanks and they are pretty easy to find. If you can find early Shaw Aero flush fuel filler caps, they look great. There are even B-17 fuel caps and fittings out there, but, of course, $$$.
I'm making a shifter that looks like a throttle quadrant, which will have 2 other levers next to it. You can always fit a P-51 stick grip on a shift lever, or -my favorite- a B-8 grip. They were used on early jets and are FULL of buttons and switches. Look at all the cockpit photos you can. Use lots of Aluminum and rivets. Paint stuff with green aircraft primer then Olive Drab... then steel wool off some of the OD paint to make it look worn.
The Douglas C-54 control wheel is a great choice -repros are available, check here-
http://www.aviation-antiques.com/index.html for lots of photos of WWII aviation stuff.
That should keep ya busy... and broke! that's the fun part right?
Dave