Okay, that's a lot of reference!! LOL!! I guess I should be careful what I ask for.
I think a good starting point would be Afrika Korps uniforms, pith helmets and boots (for the laced up look of your "Rugged Adventurer". The Doctor would do well with WWII US Marines leggings over a tropical uniform. As for the high black leather boots, German WWII is perfect, and I think easy to find. Tan or khaki pants with white shirt for the Rugged Adventurer, Reporter and Fortune Hunter. You may be able to find loose Indiana Jones fedoras on Ebay. The bowler hat will be harder to find but they're out there. A whole line of umbrella's was made by Wild Toys, also one came with the Henry Jones figure. A lot of companies are now producing civilian suits, perfect for your Padre and Professor. You can pick up belts, pouches and revolvers/holsters from the usual parters like Monkey Depot, War Toys, Toy Anxiety etc. There you can really mix and match, as you like.
I can't see your female rocketeer. But there was a full-on Rocketeer figure done some time ago, as well as Buck Rogers (very useful retro ray gun), and on that topic, I think there are 3-D printed ray guns available from Shapeways.
I hope this helps. Looks like a really fun project!