I had the same problem with missing caps. When i called Dehco I was told they were not available and there was nothing they could do. Since the dishwasher was still under warranty i told them I wanted to file a warranty claim to replace the unit since without the caps my dishwasher was leaking water. The next day Dehco seemed to find the caps and sent them to me. If yours is still under warranty you might try doing the same. Good luck.
2016 Champagne EL38
2016 Dodge Ram 3500 DWD