Roller Coaster Tycoon 3 custom supports?

So recently I've gotten into playing RCT3 again, but I don't know how to get custom supports and stuff like that. I see it all over youtube, and I've looked up some forums to try and figure it out. I know a lot of people used to use "Steelworks" or something like that, but it doesn't seem to exist anymore. I don't know of any sites to download supports. Actually, I found one. It is called "Moby Steel Jungle" or something like that, but when i try to unzip it to the specified location it gives me an "Access Denied" error. Does anyone know of sites I can get some custom supports or why I cant unzip the other files? (Also, I'm running on Windows 7)