How can I cut a coconut in half without smashing it to pieces?

Me and a few friends are having a 'not going on holiday this year so lets just pretend' party and to get into the holiday feel we're planning to make cocktails in coconuts.
Can you buy half a coconut from any supermarkets?
If not then what's the best way to cut it in half?
I don't want to end up smashing them into pieces because then we can't drink out of them.
I've asked arround and most people propose the old sledge hammer in a tea-towel technique, but obviously for my purpose this isn't going to work.
Any ideas?

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