Methods of sliding PCB in straight line on drill press
Look at the extrusion 3D printers for cheap linear shafting ideas, using either rollerblade bearings at right angles, sleeve bushings or even sleeve bearings.

However, you will then encounter a problem familiar to users of real machine tools, which is the need to align the row with the machine axis.

By the time you go for ratcheting you may just want an X-Y table, though exercise some care to get inch or metric screws with a lead-per-turn closely related to your spacing.  If you don't do that, you'll likely want to add a digital readout or even servo/stepper drive.  And then you need to learn about managing backlash.

There's a reason machine tools are expensive...