I saw an awesome little paddle trick in Czech Republic about 4 years ago. I jotted down the design after I figured out the method and made one when I got back to Canada. I've shown it to some magicians and magic shops and no one has seen it -- and they love it, it's a great paddle trick. I have no way of finding this Czech dude: he was presented at the festival prop booths who could have been from anywhere in Europe. Is it straight-up ethically/legally wrong to produce this trick with my own instructions?

In a word - Yes.

Modify the design and the routine that go with it enough and you can probably sell it. I would not use his exact handling and routine for both ethical and legal reasons.

Maybe you could get in touch with a few Czech magic clubs such as IBM or Magic Circle or something and see if they know who the man could be.

I would try to find the guy first, then maybe market the idea with your presentation and handling.