It depends what kind of adapter you're looking for.
The Honey Bee converter is just a simple plug-through adapter, so you can plug Japanese Mega Drive cartridges into a European Mega Drive or US Genesis cart slot. (You can just as easily file the edges of the cartridge slot to get the larger Jap carts to fit - it's a lot neater that way.)
What this adapter does *not* do is get around the territory protection on later (post-1992) releases. You need something like a Mega Key adapter, or switches fitted to the console itself, to do that.
Thanks, I might have a look around for one. I've only just got a new Megadrive after about 8 years without so I'm just weighing up the options really. I read on Gamefaqs that there was actually an adapter released which had the 50/60 and language switches on the back. I'm guessing they're pretty scarce now, if they even exist at all, as that's the only place I've seen them mentioned.