Japanese consoles on UK mains.

I've looked a bit on the internet and now it's your turn, I have a Japanese Megadrive II, or genesis to you americans, and it has a 100v power adaptor or whatever.

I need it to run on the UK mains.

What transformer do I buy and where, I don't want to risk smoking it.

Thanks.

and please don't write "modern consoles blah blah" this thing is from the early 90's.