Most Pokémon fans have friends, but they may not have buddies that are still rocking a Game Boy, link cable and a copy of Pokémon Red and / or Blue. After all, millions of fans have moved on to online trading and match-ups in the latest 3DS releases.
If you still like to go retro, though, a 'mon fan called Pepijn de Vos has come up with a clever workaround to allow you to trade Pokémon (and complete your Pokédex) with no-one else involved. You just need a Game Boy (or a Color / Advance), copies of Red and Blue, an Arduino board (which you can buy online) and a link cable. It seems to work by trading a 'mon with the Arduino, swapping carts and then trading once again. Ultimately, it's a way to complete trades on the original games, including access to the trickier / rarer pocket monsters.
You can read this blog post for instructions and there's a demonstration video below. If all of these online shenanigans in the new games aren't to your taste, this could be a fun little project.