One way to reproduce artwork is to simply draw or paint it again. Certainly the fine art of forgery uses this method, but here I am speaking of making copies of my own work. I use a template to simplify the drawing, but each piece, in this case each card, is an original work. They just look very similar.
I cut and fold watercolor paper to form a card then trace my template onto the watercolor paper. Nothing fancy here, I just put the template under the card and stick it to a sunny window to trace. Then I use a pen to do the actual drawing with all it’s fun details. The details vary from card to card. I drew a handy dandy suitcase-styles-reference-sheet so I don’t run out of ideas. Then I paint each one. The cards share a color pallette, but the suitcases are rarely the same color from card to card. Besides the different colors and suitcase styles, there are the inevitable variations that come from hand drawing. Although the cards share a layout, each is truly unique. When you buy one it’s a surprise just what your card will look like.