There's no shortage of Star Trek paraphernalia, but this Star Trek Hero Type-I Phaser Kit gives you exactly the same prop that was used on the original Star Trek series. You can be sure this replica will have the same look and feel of the original, because it was "molded off an original prop for perfect accuracy."
You must be handy to possess such a museum-quality object, though, because it's only available in the form of a $200 kit that you must assemble yourself. For extra authenticity, we'd say add a few extra parts to make it a full-fledged TASER, so you can set it on stun for real. Here's a pic of the various phaser parts, ready for assembly: