Copy Adjacent Cells alongside Duplicate Cells

Question

I have a very large Google Sheet spreadsheet that I need help with.

I have a long list of Network Switches that are very often repeated that I am trying to automatically copy the associated SKU into a separate adjacent cell.

My goal was, once the SKU is added the first time, whenever the same switch is added again, it will autopopulate with the same SKU.

For instance, C2461:C2463 are repeated, and once K2461 is populated, would like K2462 & K2463 to follow suit.

Any help would be greatly appreciated!