You go on eBay or similar site and you pay for a used copy on floppy or CD-ROM. Then using the appropriate tool you back those files up and use them for OpenCiv 1. Cheap, no. Convenient, no. But legal.

If you're lucky you stumble across it in a thrift store that wasn't paying particular attention and assumed it was a puzzle or a board game.

So: Yes, hopelessly naive.