Doesn't Play! Pokémon give out "official" IRL Gym Badges at Leagues and stuff? I'm not sure if that's a thing that still happens or if that was just in the past, but I'd imagine those ones would be the best and most realistic. They would likely be available on Ebay.
If you're looking for fan-made ones, there's so many people who have made them that it's probably hard to tell unless you specifically hear from someone who makes them or has bought fan-made ones in the past. I know they're a pretty popular item in Artist Booths at anime conventions and the like, so that might be an opportunity for you to see and feel them in person, if you attend any local cons anyway.