Unfortunately, there are no current adaptors available that will allow you to play a US or Japanese Game on a UK 32X system. Also, the machines themselves have to be inserted into a machine of that region too, i.e. a US 32X System will only work in a US Mega Drive (Genesis) and not in a UK Mega Drive.
If you’re eager to play the US and Japanese releases, you’ll need a Genesis, a US Sega 32X and a Japanese Mega Drive and Japanese 32X, so if you’re looking to start collecting for this machine, it’s worth bearing in mind! Alternatively, if you can find someone to add a 50hz/60hz switch to your Mega Drive, you’ll be able to use a US 32X and play US 32X Games.