You need the original game files from RCT1 (generally purchased cheaply on GOG.com or Steam). OpenRCT2 reads those files and creates a modern, portable version.
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For millions of millennials and Gen Z gamers, the sound of a marching band, the clunk of a handyman’s broom, and the terrified scream of a poorly designed corkscrew loop are the sounds of childhood. RollerCoaster Tycoon 1 (RCT1), developed by Chris Sawyer and published by Hasbro Interactive in 1999, is widely considered the gold standard of simulation games. You need the original game files from RCT1