I've seen a few requests about a certain color scheme of model X, or where to put a certain decal etc... some people might not have used this and it may seem simplistic but it has worked for me!
Go to
google.com and click on the images link at the top of the page. Type in the model you are researching. For a recent build I used SBD, SBD-5, Dauntless etc... went through all ways to designate the type pf dive bomber I wanted. Not only did I find exactly the paint scheme for almost the
exact plane I was looking for but all kinds of pics of battle damaged planes etc... that gave me tons of ideas for weathing etc...
Then I usually go back and search google again on the regular web section. You can find a lot of history of the model here, as well as specs etc for markings and such.
I know some of them are harder to come by than others but for the most part everything I have wanted has been out there! I've even found some kits either to have the wrong decal set, even an entirely wrong instrument panel on one helicopter this way! And I definitely almost always find a descrepancy on the colors they tell you to paint the things... (paint interior light grey, then go to the web and find it all done in dark grey and black in original photos from the era)
Like I said, seems a little easy and maybe everyone knew this, but if you haven't you never know what you might find!