Part of Metal Type’s Printing Advice section, here Phil discusses creating accordion folds.
If this was just an ordinary job on light weight card stock of about 9 thou; I would just comp up a form of plain old type high scoring rules and go with that. Take the ink rollers out and run the stock through with enough impression so that the card stock folds easily.
I have often used hairline brass rule for this kind of job and scored all the scores or folds from one side.
But it all depends; for example, how thick the card stock is. If the card stock is 12 thou or thicker, then this scoring with brass rule from one side only, will not work. The results will be poor and there is a lot of danger that the stock will crack instead of folding like it should.