About everything you asked about you can get on Ebay... Kits like the B-26 COINvader are pretty rare. Italeri put out a 1/72 scale version years ago, but it's not around in hobby shops anymore, so Ebay is your bedt bet. The Revell (ex monogram) A-26 can be converted, but I don't know any after-market kit for it, so it's a scratchbuilding job (Happen to be doing one now).
The old Monogram B-52D kit in 1/72, Monogram 1/48th T-28, are on Ebay fairly often.. Don'tknow about the B-47.. I know Revell made a "Box Scale" Stratojet once upon a time, back in the 50's, but those command pretty high prices now.. See here at Old Model Kits . Com
http://www.oldmodelkits.com/index.php
At the top, use the search function and pick from the menu: Military Aircraft/Any Manufacturer/Any Scale/ and then type in the text box, "B-47"
They show about 8 kits, the Old Revell one I spoke of, plus Hasegawa and Aurora...
If money is no object, then thaey will likely have any kit you want if it was ever released in plastic, but you're gonna PAY for it...
Good luck, sir