I have made my own of this type where the kit only gives the styrene panel.
I first drill out the instruments with a small drill. Then I scan the styrene panel to show exactly where the instrument holes are. This provides a template for some computer artwork. I have spent some time looking for images of various types of aircraft instruments- airspeed indicators, altimeter, attitude indicators, compasses, etc. I keep a whole folder of them, both white faced and black faced instruments.
With computer editing software, it is easy to resize for each popular scale the instrument images saved from internet. I then paste a copy of each instrument onto the template I made (the scanned image of the panel. If you paste each where the hole is, you end up with a set of instruments in the right spot. I then print this array of instruments on glossy photo paper, cut it out and glue it to the back of the styrene panel.