You don't actually need to buy the Resistance at all since it is simple to just make it.
All you need are to use the loyalty cards from your Shadows Over Camelot game to tell people secretly whether they are the traitors or not. Alternatively you could use regular playing cards with face cards being loyal and aces being traitors.
Then you need a simple up/down mechanic for voting on missions. A simple penny will work for each person as they can just use heads for yes and tails for no.
Then you need a hidden mechanic for the people on missions to vote succeed/fail. I use the turn order tokens from my Heroscape collection (with "X" being fail and "1" being succeed). But you could do this also with simple playing cards with "2" being fail and "4" being succeed, or you could use UNO cards with "Reverse" for fail and "Skip" for succeed.
So you can play Resistance simply with a basic deck of cards and some pennies. After all the fun of the game isn't really the components, but the social interplay that results.