There's probably fancy metal hairdressing combs that would do it, but the "prow" of a normal comb is too blunt to separate the hair perfectly. You end up with strands from the left on the right etc.
The old DIY trick is to turn a sharp-pointed knife upside down so that the blade doesn't face the scalp, and then use the point to gently part the hair. That's how you get a perfect straight parting.