As mentioned previously just google FSX add-ons. There's a couple good sites you'll run across.
Also, there are ways around buying a/c too. If you know how to use torrents you're set. Just go tp
btjunkie or
thepiratebay and search the names of the companies that make these add-ons. I downloaded a "mega-pack" from Carenado through btjunkie and they are the best flying, most realistic aircraft I have on FSX. There's a reason these people want money for these aircraft. It included Beech Bonanza V35 and F33, Beech Mentor T43B, Cessna 182Q, and 182RG, 210 Centurion II, U206G, Piper Archer II, Dakota and Cherokee 180 all with several different paints. I also got a nice little 152 and a bunch more. I know those aren't your target aircraft, but just quickly searching thepiratebay for
"Captain Sim" there's some larger a/c. If it's just repaints for the default FSX a/c you're after then try
simviation, there's a ton there.
Also remember to view any "readme" file that is included in the download, they typically tell you how to install the files. It can be confusing at first, so PM me if you have an questions.